View source for ICalendar

{{Short description|Computer file format for calendar information}}
{{for|Apple's calendar application, previously named iCal|Calendar (Apple)}}
{{Redirect|.ics|other uses|ICS (disambiguation){{!}}ICS}}
{{lowercase title}}
{{infobox file format
| icon          = 
| logo          = 
| screenshot    = 
| caption       = 
| extension     = .ical, .ics, .ifb, .icalendar
| mime          = text/calendar
| type code     = 
| uniform type  = 
| magic         = 
| owner         = 
| genre         = [[Calendar]] data exchange
| container for = 
| contained by  = 
| extended from = 
| extended to   = 
| standard      = {{IETF RFC|5545|link=no}} (Updated by: {{IETF RFC|5546|link=no}}, {{IETF RFC|6868|link=no}}, {{IETF RFC|7529|link=no}}, {{IETF RFC|7986|link=no}})
| open          = Yes
}}

The '''Internet Calendaring and Scheduling Core Object Specification''' ('''iCalendar''') is a [[media type]] which allows users to store and exchange calendaring and scheduling information such as events, to-dos, journal entries, and free/busy information,<ref name=":0">{{cite IETF|editor-first=Bernard|editor-last=Desruisseaux|rfc=5545|date=September 2009|access-date=2018-12-07|publisher=[[Internet Engineering Task Force]]|title=Internet Calendaring and Scheduling Core Object Specification (iCalendar)|url=https://icalendar.org/RFC-Specifications/iCalendar-RFC-5545/}}</ref> and together with its associated standards has been a cornerstone of the standardization and interoperability of [[digital calendar]]s across different vendors. Files formatted according to the specification usually have an [[Filename extension|extension]] of {{mono|.ics}}. With supporting software, such as an [[email client|email reader]] or [[Calendaring software|calendar application]], recipients of an iCalendar data file can respond to the sender easily or counter-propose another meeting date/time. The file format is specified in a [[Internet standard|proposed Internet standard]] (RFC 5545) for calendar data exchange. The standard and file type are sometimes referred to as "iCal", which was the name of the [[Apple Inc.]] calendar program until 2012 (see [[iCal]]), which provides one of the implementations of the standard.

iCalendar is used and supported by many products, including:
* general consumer: [[Calendar (Apple)|Apple Calendar]] (formerly iCal), [[eM Client]], [[Google Calendar]], [[Yahoo! Calendar]]
* corporate: [[HCL Domino]] (formerly IBM Notes and Lotus Notes)<ref>{{cite web | url = http://www.ibm.com/developerworks/lotus/library/notes85-icalendar/index.html | title = IBM Lotus Notes 8.5 iCalendar: Interoperability, implementation, and application | publisher = IBM DeveloperWorks | access-date = 2015-04-05}}</ref>
* [[free software]]: [[GNOME Evolution]], [[GNU Emacs]], [[Mozilla Thunderbird]], and [[SeaMonkey]] 
It is partially supported by [[Microsoft Outlook]] and [[Novell GroupWise]].

iCalendar is designed to be independent of the transport protocol. For example, certain events can be sent by traditional email or whole calendar files can be shared and edited by using a [[WebDav]] server, or [[SyncML]]. Simple web servers (using just the HTTP protocol) are often used to distribute iCalendar data about an event and to publish busy times of an individual. Publishers can embed iCalendar data in web pages using [[hCalendar]], a 1:1 [[microformats|microformat]] representation of iCalendar in semantic [[XHTML|(X)]][[HTML]].

== History ==
[[file:ICalendarSpecification.png|thumb|iCalendar components and their properties]]

iCalendar was created in 1998<ref>{{cite web | url = https://icalendar.org/ | title = iCalendar.org | publisher = Z Content | access-date = 2018-03-28}}</ref> by the Calendaring and Scheduling Working Group of the [[Internet Engineering Task Force]], chaired by Anik Ganguly of [[Open Text Corporation]], and was authored by Frank Dawson of [[Lotus Development Corporation]] and Derik Stenerson of [[Microsoft Corporation]]. iCalendar data files are [[plain text]] files with the [[filename extension|extension]] {{mono|.ics}} or {{mono|.ifb}} (for files containing availability information only). RFC 5545 replaced RFC 2445 in September 2009 and now defines the standard.

iCalendar is heavily based on the earlier vCalendar by the [[Internet Mail Consortium]] (IMC) which has the {{mono|.vcs}} file extension.<ref>{{cite web | url = http://www.imc.org/pdi/vcal-10.txt | title = vCalendar: The Electronic Calendaring and Scheduling Exchange Format, Version 1.0 | date = 1996-09-18 | publisher = [[Internet Mail Consortium]] | archive-url = https://web.archive.org/web/20160321023312/https://www.imc.org/pdi/vcal-10.txt | archive-date = 2016-03-21 | url-status = dead | access-date = 2018-03-28}}</ref> After iCalendar was released, the Internet Mail Consortium stated that it "hopes that all vCalendar developers take advantage of these new open standards and make their software compatible with both vCalendar 1.0 and iCalendar."<ref>{{cite web | url = https://www.imc.org/pdi/ | title = vCalendar: The Basis for Cross-Platform Scheduling | publisher = [[Internet Mail Consortium]] | date = 2006-11-26 | url-status = dead | archive-url = https://web.archive.org/web/20150906130553/http://www.imc.org/pdi/ | archive-date = 2015-09-06 | access-date = 2016-02-28 }}</ref>

The memo "Calendar Access Protocol" ([[Request for Comments|RFC]] 4324) was an initial attempt at a universal system to create real-time calendars, but was eventually abandoned. Instead, iCalendar saw some adoption for such purposes with ''ad hoc'' extensions such as GroupDAV and [[CalDAV]] emerging as informal standards and seeing some adoption in both client and server [[software]] packages.

A first effort to simplify iCalendar standards by the [[IETF]] "Calendaring and Scheduling Working Group" (ietf-calsify WG) ended in January 2011 without seeing adoption.<ref>{{cite web|url=https://datatracker.ietf.org/wg/calsify/charter/|title=Calendaring and Scheduling Standards Simplification (calsify)|publisher=[[IETF]]|access-date=2015-04-05}}</ref><ref>{{cite web|url=http://lists.osafoundation.org/pipermail/ietf-calsify/2010-December/002272.html|title=the end of calsify working group– not the end of the mailing list|last=Lear|first=Eliot|date=2010-12-10|work=ietf-calsify mailing list|access-date=2015-04-05|archive-date=2012-12-09|archive-url=https://web.archive.org/web/20121209115511/http://lists.osafoundation.org/pipermail/ietf-calsify/2010-December/002272.html|url-status=dead}}</ref> The work was then picked up by the "Calendaring Extensions Working Group" (ietf-calext WG).<ref>{{cite web|url=https://datatracker.ietf.org/wg/calext/charter/|title=Calendaring Extensions (calext)|publisher=[[IETF]]|access-date=2016-12-01}}</ref>

== Design ==
iCalendar data have the [[MIME]] content type {{code|text/calendar}}. The filename extension of {{mono|ics}} is to be used for files containing calendaring and scheduling information, {{mono|ifb}} for files with free or busy time information consistent with this MIME content type. The equivalent file [[type code]]s in Apple Macintosh operating system environments are {{mono|iCal}} and {{mono|iFBf}}.

By default, iCalendar uses the [[UTF-8]] [[character set]]; a different character set can be specified using the "charset" MIME parameter (if the transport method used supports MIME, such as [[Email]] or [[HTTP]]). Each line is terminated by [[Carriage return|CR]]+[[Line feed|LF]] (in [[hexadecimal]]: {{mono|0D0A}}). Lines should be limited to 75 [[Octet (computing)|octets]] (not characters) long. Where a data item is too long to fit on a single line it can be continued on following lines by starting the continuation lines with a space character (in hex: 20) or a tab character (in hex: 09). Actual line feeds in data items are encoded as a backslash followed by the letter n or N (the bytes {{mono|5C 6E}} or {{mono|5C 4E}} in UTF-8).

The iCalendar format is designed to transmit calendar-based data, such as events, and intentionally does not describe what to do with that data. Thus, other programming may be needed to negotiate what to do with this data. A companion standard, "iCalendar Transport-Independent Interoperability" (iTIP) (RFC 2446), defines a protocol for exchanging iCalendar objects for collaborative calendaring and scheduling between "Calendar Users" (CUs) facilitated by an "Organizer" initiating the exchange of data. This standard defines methods such as {{code|PUBLISH}}, {{code|REQUEST}}, {{code|REPLY}}, {{code|ADD}}, {{code|CANCEL}}, {{code|REFRESH}}, {{code|COUNTER}} (to negotiate a change in the entry), and {{code|DECLINE-COUNTER}} (to decline the counter-proposal). Another companion standard, "iCalendar Message-based Interoperability Protocol (iMIP)" (RFC 2447), defines a standard method for implementing iTIP on standard Internet email-based transports. The "Guide to Internet Calendaring" (RFC 3283) explains how iCalendar interacts with other calendar computer language (current and future).

The top-level element in iCalendar is the Calendaring and Scheduling Core Object, a collection of calendar and scheduling information. Typically, this information will consist of a single iCalendar object. However, multiple iCalendar objects can be grouped together. The first line must be {{code|BEGIN:VCALENDAR}}, and the last line must be {{code|END:VCALENDAR}}; the contents between these lines is called the "icalbody". The body must include the "{{mono|PRODID}}" and "{{mono|VERSION}}" calendar properties. In addition, it must include at least one calendar component.<ref>{{cite IETF|rfc=5545|section=3.6|title=Internet Calendaring and Scheduling Core Object Specification (iCalendar)|sectionname=Section 3.6 Calendar Components|access-date=1 July 2020}}</ref>

{{code|VERSION:1.0}} is used to specify that data is in the old vCalendar format. {{mono|VERSION}} is 2.0 for the current iCalendar format as of 2016.

The body of the iCalendar object (the icalbody) contains single-line ''Calendar Properties'' that apply to the entire calendar, as well as one or more blocks of multiple lines that each define a ''Calendar Component'' such as an event, journal entry, alarm, or one of several other types. Here is a simple example of an iCalendar object with a single calendar containing a single ''Calendar Component'', a "[[Bastille Day]] Party" event starting at 5pm on July 14, 1997, and ending at 4am the following morning:<ref>From RFC 2445</ref>

<syntaxhighlight lang="text">
BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//hacksw/handcal//NONSGML v1.0//EN
BEGIN:VEVENT
UID:uid1@example.com
ORGANIZER;CN=John Doe:MAILTO:john.doe@example.com
DTSTAMP:19970701T100000Z
DTSTART:19970714T170000Z
DTEND:19970715T040000Z
SUMMARY:Bastille Day Party
GEO:48.85299;2.36885
END:VEVENT
END:VCALENDAR
</syntaxhighlight>

The UID field distributes updates when a scheduled event changes. When the event is first generated a [[UUID|globally unique]] identifier is created. If a later event is distributed with the same UID, it replaces the original one. An example UID might be <code>Y2007S2C131M5@example.edu</code>, for the 5th meeting of class 131 in semester 2 at a hypothetical college. Email-style UIDs are now considered bad practice, with a [[UUID]] recommended instead.<ref>{{cite IETF|rfc=7986|section=5.3|title=iCalendar Property Extensions|sectionname=UID Property|access-date=3 October 2022}}</ref>

The most common representation of date and time is a ''tz timestamp'' based on [[ISO 8601]] format, such as {{mono|20010911T124640Z}}, with the format {{mono|<year (4 digits)><month (2)><day (2)>T<hour (2)><minute (2)><second (2)>Z}} for a total fixed length of 16 characters. ''Z'' indicates the use of [[Coordinated Universal Time#Time zones|UTC]] (referring to its Zulu time zone).<ref>{{cite IETF|rfc=5545|section=3.3.5|title=Internet Calendaring and Scheduling Core Object Specification (iCalendar)|sectionname=Section 3.3.5 Date-Time}}</ref> When used in {{mono|DTSTART}} and {{mono|DTEND}} properties, start times are inclusive while end times are not. This allows an event's end time to be the same as a consecutive event's start without those events overlapping and potentially creating (false) scheduling conflicts.<ref>{{cite IETF|rfc=5545|section=3.6.1|title=Internet Calendaring and Scheduling Core Object Specification (iCalendar)|sectionname=Section 3.6.1 Event Components}}</ref>

Components include:

* {{mono|VEVENT}} describes an event, which has a scheduled amount of time on a calendar. Normally, when a user accepts the calendar event, this will cause that time to be considered busy, though an event can be set to be {{mono|TRANSPARENT}} to change this interpretation. A {{mono|VEVENT}} may include a {{mono|VALARM}} which allows an alarm. Such events have a {{mono|DTSTART}} which sets a starting time, and a {{mono|DTEND}} which sets an ending time. If the calendar event is recurring, {{mono|DTSTART}} sets up the start of the first event.
* {{mono|VTODO}} explains a to-do item, i.e., an action-item or assignment. Not all calendar applications recognize {{mono|VTODO}} items. In particular, Outlook does not export Tasks as {{mono|VTODO}} items, and ignores {{mono|VTODO}} items in imported calendars.<ref>{{cite web|url=https://msdn.microsoft.com/en-us/library/ee624464%28v=exchg.80%29.aspx|website=Microsoft Developer Network|title=[RFC5546] Section 3.4 Methods for VTODO Components|access-date=7 August 2015}}</ref>
* {{mono|VJOURNAL}} is a journal entry. They attach descriptive text to a particular calendar date, may be used to record a daily record of activities or accomplishments, or describe progress with a related to-do entry. A {{mono|VJOURNAL}} calendar component does not take up time on a calendar, so it has no effect on free or busy time (just like {{mono|TRANSPARENT}} entries). In practice, few programs support {{mono|VJOURNAL}} entries.
* {{mono|VFREEBUSY}} is a request for free/busy time, is a response to a request, or is a published set of busy time.{{Clarify|date=December 2008}}
* Other component types include {{mono|VAVAILABILITY}}, {{mono|VTIMEZONE}} (time zones) and {{mono|VALARM}} (alarms). Some components can include other components ({{mono|VALARM}} is often included in other components). Some components are often defined to support other components defined after them ({{mono|VTIMEZONE}} is often used this way).{{Clarify|date=December 2008}}

iCalendar is meant to "provide the definition of a common format for openly exchanging calendaring and scheduling information across the Internet". While the features most often used by users are widely supported by iCalendar, some more advanced capabilities have problems. For example, most vendors do not support Journals ({{mono|VJOURNAL}}). {{mono|VTODO}}s have had conversion problems as well.<ref>CalConnect, 2004</ref>

iCalendar's calendar is also not compatible with some non-[[Gregorian calendar|Gregorian]] calendars such as the [[lunar calendar]]s used in [[Israel]] and [[Saudi Arabia]]. Although there exist one-to-one mappings between Gregorian and many other calendar scales, the lack of defined {{mono|CALSCALE}} values for those calendars and limitations in various date fields can make native support impossible. For example the [[Hebrew calendar]] year may contain either 12 or 13 months, and the [[Japanese era name|Japanese]] Emperor-based calendar scale contains many eras.

== Extensions ==
vCalendar and iCalendar support private [[software extensions]], with a "X-" prefix, a number of which are in common usage.

Some of these include:

* <code>X-RECURRENCE-ID</code>: vCalendar 1.0 extension which mimics the iCalendar 2.0 RECURRENCE-ID (Nokia S60 3rd Edition)
* <code>X-EPOCAGENDAENTRYTYPE</code>: defines the client calendar type
* <code>X-FUNAMBOL-AALARMOPTIONS</code>
* <code>X-FUNAMBOL-ALLDAY</code>: All Day event flag
* <code>X-MICROSOFT-CDO-ALLDAYEVENT</code>: Microsoft Outlook all day event flag
* <code>[https://learn.microsoft.com/en-us/openspecs/exchange_server_protocols/ms-oxcical/cd68eae7-ed65-4dd3-8ea7-ad585c76c736 X-MICROSOFT-CDO-BUSYSTATUS]</code>: Microsoft Outlook status information
* <code>[https://learn.microsoft.com/en-us/openspecs/exchange_server_protocols/ms-oxcical/df1c7988-9908-4ee6-95b0-fcd180b02b44 X-MICROSOFT-CDO-INTENDEDSTATUS]</code>
* <code>X-WR-CALNAME</code>: The display name of the calendar
* <code>X-WR-CALDESC</code>: A description of the calendar
* <code>X-WR-RELCALID</code>: A globally unique identifier for the calendar<ref>{{Cite web|title = [MS-OXCICAL]: Property: X-WR-RELCALID|url = https://msdn.microsoft.com/en-us/library/ee179588(v=exchg.80).aspx|website = msdn.microsoft.com|access-date = 2016-02-23}}</ref>
* <code>X-WR-TIMEZONE</code>
* <code>X-PUBLISHED-TTL</code>: Recommended update interval for subscription to the calendar
* <code>X-ALT-DESC</code>: Used to include HTML markup in an event's description. Standard DESCRIPTION tag should contain non-HTML version.
* <code>X-FMTTYPE</code>, <code>X-FILEDATE</code>, <code>X-NAME</code>, <code>X-CN</code>, <code>X-STATUS</code>,  <code>X-ROLE</code>, <code>X-SENTBY</code>, <code>X-SYMBIAN-DTSTAMP</code>, <code>X-METHOD</code>, <code>X-RECURRENCE-ID</code>, <code>X-EPOCALARM</code>, <code>X-SYMBIAN-LUID</code>, <code>X-EPOCAGENDAENTRYTYPE</code><ref>{{Cite web |date=October 8, 2009 |others=© [[Nokia Corporation]] 2011 |title=iCal and vCal Properties |url=http://devlib.symbian.slions.net/s3/GUID-7811C33D-96D3-5001-B4D3-92BF44F39B2C.html |url-status=live |archive-url=https://web.archive.org/web/20210509022426/http://devlib.symbian.slions.net/s3/GUID-7811C33D-96D3-5001-B4D3-92BF44F39B2C.html |archive-date=May 9, 2021 |access-date=2023-11-17 |website=Nokia Symbian^3 Developer's Library v1.1 |language=en}}</ref><!-- TODO: figure out how to understand and make better use of this source -->

== List of components, properties, and parameters ==
{| class="wikitable sortable mw-collapsible"
|-
! Name 
! Kind
! RFC section (RFC 5545<ref name=":0" />{{Rp|pages=155–159|location=section 8.3|page=}} by default)
! MS-OXCICAL section 2.1.3<ref name=":1">{{Cite web |last= |date=2020-10-13 |title=[MS-OXCICAL]: 2.1.3 Processing Rules |url=https://learn.microsoft.com/en-us/openspecs/exchange_server_protocols/ms-oxcical/74d3bf60-f30d-4fca-84d3-cfd04da8e627 |url-status=live |archive-url=https://web.archive.org/web/20231116165430/https://learn.microsoft.com/en-us/openspecs/exchange_server_protocols/ms-oxcical/74d3bf60-f30d-4fca-84d3-cfd04da8e627 |archive-date=2023-11-16 |access-date=2023-11-16 |website=learn.microsoft.com |language=en-us}}</ref> subsections
|-
| VCALENDAR
| Component
| 3.4. iCalendar Object
| 1.1
|-
| VEVENT
| Component
| 3.6.1. Event Component
| 1.1.20
|-
| VTODO
| Component
| 3.6.2. To-Do Component
| 
|-
| VJOURNAL
| Component
| 3.6.3. Journal Component
| 
|-
| VFREEBUSY
| Component
| 3.6.4. Free/Busy Component
| 
|-
| VTIMEZONE
| Component
| 3.6.5. Time Zone Component
| 
|-
| STANDARD
| Component
| 3.6.5. Time Zone Component
| 1.1.19.2
|-
| DAYLIGHT
| Component
| 3.6.5. Time Zone Component
| 1.1.19.3
|-
| VALARM
| Component
| 3.6.6. Alarm Component
| 
|-
| VAVAILABILITY
| Component
| RFC 7953 section 3.1. VAVAILABILITY Component
| 
|-
| AVAILABLE
| Component
| RFC 7953 section 3.1. VAVAILABILITY Component
| 
|-
| PARTICIPANT
| Component
| RFC 9073 section 7.1. Participant
| 
|-
| VLOCATION
| Component
| RFC 9073 section 7.2. Location
| 
|-
| VRESOURCE
| Component
| RFC 9073 section 7.3. Resource
| 
|-
| CALSCALE 
| Property
| 3.7.1. Calendar Scale
| 
|-
| METHOD 
| Property
| 3.7.2. Method
| 1.1.1
|-
| PRODID 
| Property
| 3.7.3. Product Identifier
| 1.1.2
|-
| VERSION 
| Property
| 3.7.4. Version
| 1.1.3
|-
| X-CALEND
| Property
| 
| 1.1.4
|-
| X-CALSTART
| Property
| 
| 1.1.5
|-
| X-CLIPEND
| Property
| 
| 1.1.6
|-
| X-CLIPSTART
| Property
| 
| 1.1.7
|-
| X-MICROSOFT-CALSCALE
| Property
| 
| 1.1.8
|-
| X-MS-OLK-FORCEINSPECTOROPEN
| Property
| 
| 1.1.9
|-
| X-MS-WKHRDAYS
| Property
| 
| 1.1.10
|-
| X-MS-WKHREND
| Property
| 
| 1.1.11
|-
| X-MS-WKHRSTART
| Property
| 
| 1.1.12
|-
| X-OWNER
| Property
| 
| 1.1.13
|-
| X-PRIMARY-CALENDAR
| Property
| 
| 1.1.14
|-
| X-PUBLISHED-TTL
| Property
| 
| 1.1.15
|-
| X-WR-CALDESC 
| Property
| 
| 1.1.16
|-
| X-WR-CALNAME 
| Property
| 
| 1.1.17
|-
| X-WR-RELCALID 
| Property
| 
| 1.1.18
|-
| ATTACH 
| Property
| 3.8.1.1. Attachment
| 1.1.20.1
|-
| CATEGORIES 
| Property
| 3.8.1.2. Categories, RFC 7986 section 5.6. CATEGORIES Property
| 1.1.20.3
|-
| CLASS 
| Property
| 3.8.1.3. Classification
| 1.1.20.4
|-
| COMMENT 
| Property
| 3.8.1.4. Comment
| 1.1.20.5
|-
| DESCRIPTION 
| Property
| 3.8.1.5. Description, RFC 7986 section 5.2. DESCRIPTION Property
| 1.1.20.11, 1.1.20.62.3
|-
| GEO 
| Property
| 3.8.1.6. Geographic Position
| 
|-
| LOCATION 
| Property
| 3.8.1.7. Location
| 1.1.20.15
|-
| PERCENT-COMPLETE 
| Property
| 3.8.1.8. Percent Complete
| 
|-
| PRIORITY 
| Property
| 3.8.1.9. Priority
| 1.1.20.17
|-
| RESOURCES 
| Property
| 3.8.1.10. Resources
| 1.1.20.21
|-
| STATUS 
| Property
| 3.8.1.11. Status
| 1.1.20.23
|-
| SUMMARY 
| Property
| 3.8.1.12. Summary
| 1.1.20.24
|-
| COMPLETED 
| Property
| 3.8.2.1. Date-Time Completed
| 
|-
| DTEND 
| Property
| 3.8.2.2. Date-Time End
| 1.1.20.8
|-
| DUE 
| Property
| 3.8.2.3. Date-Time Due
| 
|-
| DTSTART 
| Property
| 3.8.2.4. Date-Time Start
| 1.1.19.2.1, 1.1.19.3.1, 1.1.20.10
|-
| DURATION 
| Property
| 3.8.2.5. Duration
| 1.1.20.12
|-
| FREEBUSY 
| Property
| 3.8.2.6. Free/Busy Time
| 
|-
| TRANSP 
| Property
| 3.8.2.7. Time Transparency
| 1.1.20.25
|-
| TZID 
| Property
| 3.8.3.1. Time Zone Identifier
| 1.1.19.1
|-
| TZNAME 
| Property
| 3.8.3.2. Time Zone Name
| 1.1.19.2.3, 1.1.19.3.3
|-
| TZOFFSETFROM 
| Property
| 3.8.3.3. Time Zone Offset From
| 1.1.19.2.4, 1.1.19.3.4
|-
| TZOFFSETTO 
| Property
| 3.8.3.4. Time Zone Offset To
| 1.1.19.2.5, 1.1.19.3.5
|-
| TZURL 
| Property
| 3.8.3.5. Time Zone URL
| 
|-
| ATTENDEE 
| Property
| 3.8.4.1. Attendee
| 1.1.20.2
|-
| CONTACT 
| Property
| 3.8.4.2. Contact
| 1.1.20.6
|-
| ORGANIZER 
| Property
| 3.8.4.3. Organizer
| 1.1.20.16
|-
| RECURRENCE-ID 
| Property
| 3.8.4.4. Recurrence ID
| 1.1.20.20
|-
| RELATED-TO 
| Property
| 3.8.4.5. Related To, RFC 9253 section 9.1. RELATED-TO
| 
|-
| URL 
| Property
| 3.8.4.6. Uniform Resource Locator, RFC 7986 section 5.5. URL Property
| 
|-
| UID 
| Property
| 3.8.4.7. Unique Identifier, RFC 7986 section 5.3. UID Property
| 1.1.20.26
|-
| EXDATE 
| Property
| 3.8.5.1. Exception Date-Times
| 1.1.20.13
|-
| RDATE 
| Property
| 3.8.5.2. Recurrence Date-Times
| 1.1.20.18
|-
| RRULE 
| Property
| 3.8.5.3. Recurrence Rule
| 1.1.19.2.2, 1.1.19.3.2, 1.1.20.19
|-
| ACTION 
| Property
| 3.8.6.1. Action
| 1.1.20.62.2
|-
| REPEAT 
| Property
| 3.8.6.2. Repeat Count
| 
|-
| TRIGGER 
| Property
| 3.8.6.3. Trigger
| 1.1.20.62.1
|-
| CREATED 
| Property
| 3.8.7.1. Date-Time Created
| 1.1.20.7
|-
| DTSTAMP 
| Property
| 3.8.7.2. Date-Time Stamp
| 1.1.20.9
|-
| LAST-MODIFIED 
| Property
| 3.8.7.3. Last Modified, RFC 7986 section 5.4. LAST-MODIFIED Property
| 1.1.20.14
|-
| SEQUENCE 
| Property
| 3.8.7.4. Sequence Number
| 1.1.20.22
|-
| REQUEST-STATUS 
| Property
| 3.8.8.3. Request Status
| 
|-
| X-ALT-DESC
| Property
| 
| 1.1.20.27
|-
| X-MICROSOFT-CDO-ALLDAYEVENT
| Property
| 
| 1.1.20.28
|-
| X-MICROSOFT-CDO-APPT-SEQUENCE
| Property 
| 
| 1.1.20.29
|-
| X-MICROSOFT-CDO-ATTENDEE-CRITICAL-CHANGE
| Property 
| 
| 1.1.20.30
|-
| X-MICROSOFT-CDO-BUSYSTATUS
| Property 
| 
| 1.1.20.31
|-
| X-MICROSOFT-CDO-IMPORTANCE
| Property 
| 
| 1.1.20.32
|-
| X-MICROSOFT-CDO-INSTTYPE
| Property 
| 
| 1.1.20.33
|-
| X-MICROSOFT-CDO-INTENDEDSTATUS
| Property 
| 
| 1.1.20.34
|-
| X-MICROSOFT-CDO-OWNERAPPTID
| Property 
| 
| 1.1.20.35
|-
| X-MICROSOFT-CDO-OWNER-CRITICAL-CHANGE
| Property 
| 
| 1.1.20.36
|-
| X-MICROSOFT-CDO-REPLYTIME
| Property 
| 
| 1.1.20.37
|-
| X-MICROSOFT-DISALLOW-COUNTER
| Property 
| 
| 1.1.20.38
|-
| X-MICROSOFT-EXDATE
| Property 
| 
| 1.1.20.39
|-
| X-MICROSOFT-ISDRAFT
| Property 
| 
| 1.1.20.40
|-
| X-MICROSOFT-MSNCALENDAR-ALLDAYEVENT
| Property 
| 
| 1.1.20.41
|-
| X-MICROSOFT-MSNCALENDAR-BUSYSTATUS
| Property 
| 
| 1.1.20.42
|-
| X-MICROSOFT-MSNCALENDAR-IMPORTANCE
| Property 
| 
| 1.1.20.43
|-
| X-MICROSOFT-MSNCALENDAR-INTENDEDSTATUS
| Property 
| 
| 1.1.20.44
|-
| X-MICROSOFT-RRULE
| Property 
| 
| 1.1.20.45
|-
| X-MS-OLK-ALLOWEXTERNCHECK
| Property 
| 
| 1.1.20.46
|-
| X-MS-OLK-APPTLASTSEQUENCE
| Property 
| 
| 1.1.20.47
|-
| X-MS-OLK-APPTSEQTIME
| Property 
| 
| 1.1.20.48
|-
| X-MS-OLK-AUTOFILLLOCATION
| Property 
| 
| 1.1.20.49
|-
| X-MS-OLK-AUTOSTARTCHECK
| Property 
| 
| 1.1.20.50
|-
| X-MS-OLK-COLLABORATEDOC
| Property 
| 
| 1.1.20.51
|-
| X-MS-OLK-CONFCHECK
| Property 
| 
| 1.1.20.52
|-
| X-MS-OLK-CONFTYPE
| Property 
| 
| 1.1.20.53
|-
| X-MS-OLK-DIRECTORY
| Property 
| 
| 1.1.20.54
|-
| X-MS-OLK-MWSURL
| Property 
| 
| 1.1.20.55
|-
| X-MS-OLK-NETSHOWURL
| Property 
| 
| 1.1.20.56
|-
| X-MS-OLK-ONLINEPASSWORD
| Property 
| 
| 1.1.20.57
|-
| X-MS-OLK-ORGALIAS
| Property 
| 
| 1.1.20.58
|-
| X-MS-OLK-SENDER
| Property 
| 
| 1.1.20.61
|-
| BUSYTYPE
| Property
| RFC 7953 section 3.2. Busy Time Type
| 
|-
| NAME
| Property
| RFC 7986 section 5.1. NAME Property
| 
|-
| REFRESH-INTERVAL
| Property
| RFC 7986 section 5.7. REFRESH-INTERVAL Property
| 
|-
| SOURCE
| Property
| RFC 7986 section 5.8. SOURCE Property
| 
|-
| COLOR
| Property
| RFC 7986 section 5.9. COLOR Property
| 
|-
| IMAGE
| Property
| RFC 7986 section 5.10. IMAGE Property
| 
|-
| CONFERENCE
| Property
| RFC 7986 section 5.11. CONFERENCE Property
| 
|-
| CALENDAR-ADDRESS
| Property
| RFC 9073 section 6.4. Calendar Address
| 
|-
| LOCATION-TYPE
| Property
| RFC 9073 section 6.1. Location Type
| 
|-
| PARTICIPANT-TYPE
| Property
| RFC 9073 section 6.2. Participant Type
| 
|-
| RESOURCE-TYPE
| Property
| RFC 9073 section 6.3. Resource Type
| 
|-
| STRUCTURED-DATA
| Property
| RFC 9073 section 6.6. Structured-Data
| 
|-
| STYLED-DESCRIPTION
| Property
| RFC 9073 section 6.5. Styled-Description
| 
|-
| ACKNOWLEDGED
| Property
| RFC 9074 section 6.1. Acknowledged Property
| 
|-
| PROXIMITY
| Property
| RFC 9074 section 8.1. Proximity Property
| 
|-
| CONCEPT
| Property
| RFC 9253 section 8.1. Concept
| 
|-
| LINK
| Property
| RFC 9253 section 8.2. Link
| 
|-
| REFID
| Property
| RFC 9253 section 8.3. Refid
| 
|-
| ALTREP
| Parameter 
| 3.2.1. Alternate Text Representation
| 1.1.20.15.1
|-
| CN
| Parameter 
| 3.2.2. Common Name
| 1.1.13.1, 1.1.20.2.1, 1.1.20.16.1, 1.1.20.61.1
|-
| CUTYPE
| Parameter 
| 3.2.3. Calendar User Type
| 1.1.20.2.2
|-
| DELEGATED-FROM
| Parameter 
| 3.2.4. Delegators
| 
|-
| DELEGATED-TO
| Parameter 
| 3.2.5. Delegatees
| 
|-
| DIR
| Parameter 
| 3.2.6. Directory Entry Reference
| 
|-
| ENCODING
| Parameter 
| 3.2.7. Inline Encoding
| 1.1.20.1.1
|-
| FMTTYPE
| Parameter 
| 3.2.8. Format Type
| 1.1.20.1.2, 1.1.20.27.1
|-
| FBTYPE
| Parameter 
| 3.2.9. Free/Busy Time Type
| 
|-
| LANGUAGE
| Parameter 
| 3.2.10. Language
| 1.1.20.11.1, 1.1.20.15.2, 1.1.20.24.1
|-
| MEMBER
| Parameter 
| 3.2.11. Group or List Membership
| 
|-
| PARTSTAT
| Parameter 
| 3.2.12. Participation Status
| 1.1.20.2.3
|-
| RANGE
| Parameter 
| 3.2.13. Recurrence Identifier Range
| 
|-
| RELATED
| Parameter 
| 3.2.14. Alarm Trigger Relationship
| 
|-
| RELTYPE
| Parameter 
| 3.2.15. Relationship Type, RFC 9074 section 7.1. Relationship Type Property Parameter, RFC 9253 sections 4 and 5
| 
|-
| ROLE
| Parameter 
| 3.2.16. Participation Role
| 1.1.20.2.4
|-
| RSVP
| Parameter 
| 3.2.17. RSVP Expectation
| 1.1.20.2.5
|-
| SENT-BY
| Parameter 
| 3.2.18. Sent By
| 
|-
| TZID
| Parameter 
| 3.2.19. Time Zone Identifier
| 1.1.4.1, 1.1.5.1, 1.1.6.1, 1.1.7.1, 1.1.11.1, 1.1.12.1, 1.1.20.8.1, 1.1.20.9.1, 1.1.20.10.1, 1.1.20.13.1, 1.1.20.18.1, 1.1.20.20.1, 1.1.20.48.1
|-
| VALUE
| Parameter 
| 3.2.20. Value Data Types
| 1.1.20.1.3, 1.1.20.8.2, 1.1.20.10.2, 1.1.20.13.2, 1.1.20.18.2, 1.1.20.20.2, 1.1.20.39.1, 1.1.20.45.1
|-
| X-FILENAME
| Parameter
| 
| 1.1.20.1.4
|-
| X-MS-OLK-RESPTIME
| Parameter
| 
| 1.1.20.2.6
|-
| X-MICROSOFT-ISLEAPMONTH
| Parameter
| 
| 1.1.20.45.2
|-
| DISPLAY
| Parameter
| RFC 7986 section 6.1. DISPLAY Property Parameter
| 
|-
| EMAIL
| Parameter
| RFC 7986 section 6.2. EMAIL Property Parameter
| 
|-
| FEATURE
| Parameter
| RFC 7986 section 6.3. FEATURE Property Parameter
| 
|-
| LABEL
| Parameter
| RFC 7986 section 6.4. LABEL Property Parameter
| 
|-
| ORDER
| Parameter
| RFC 9073 section 5.1. Order
| 
|-
| SCHEMA
| Parameter
| RFC 9073 section 5.2. Schema
| 
|-
| DERIVED
| Parameter
| RFC 9073 section 5.3. Derived
| 
|-
| GAP
| Parameter
| RFC 9253 section 6.2. Gap
| 
|-
| LINKREL
| Parameter
| RFC 9253 section 6.1. Link Relation
| 
|}

== Other representations ==
[[xCal]] is an [[XML]] representation of iCalendar data, as defined in {{IETF RFC|6321}}.

jCal is a [[JSON]] representation of iCalendar data, as defined in {{IETF RFC|7265}}.

[[hCalendar]] is an [[(X)HTML|(x)HTML]] representation of a subset of iCalendar data using [[microformat]]s.

hEvent is an HTML representation of a subset of iCalendar data using [[microformat]]s addressing some accessibility concerns with the hCalendar format.

== See also ==
* {{annotated link|CalDAV}}
* {{annotated link|vCard}}

== References ==
{{reflist}}

== External links ==
* {{IETF RFC|5545|link=no}} Internet Calendaring and Scheduling Core Object Specification (iCalendar) (replaces {{IETF RFC|2445|link=no}})
* {{IETF RFC|5546|link=no}} iCalendar Transport-Independent Interoperability Protocol (iTIP) (replaces {{IETF RFC|2446|link=no}})
* {{IETF RFC|6047|link=no}} iCalendar Message-Based Interoperability Protocol (iMIP) (replaces {{IETF RFC|2447|link=no}})
* {{IETF RFC|6321|link=no}} xCal: The XML format for iCalendar (iCalendar XML Representation)
* {{IETF RFC|6868|link=no}} update of the data formats for including certain characters, forbidden by the existing specification, in parameter values
* {{IETF RFC|7265|link=no}} jCal: The JSON Format for iCalendar
* {{IETF RFC|7953|link=no}} Calendar Availability
* {{IETF RFC|7986|link=no}} New Properties for iCalendar (additional properties to the iCalendar specification)
* {{IETF RFC|9073|link=no}} Event Publishing Extensions to iCalendar
* {{IETF RFC|9074|link=no}} "VALARM" Extensions for iCalendar
* {{IETF RFC|9253|link=no}} Support for iCalendar Relationships
* {{cite web | url = http://www.calconnect.org/resources/introduction-internet-calendaring | title = An Introduction to Internet Calendaring and Scheduling | date = 2011-10-20 | publisher = [[CalConnect]]}}
* {{cite web | url = https://icalendar.org/resources.html | title = iCalendar Resources}}: A list of resources for iCalendar and related standards.

[[Category:Computer file formats]]
[[Category:Calendaring standards]]
[[Category:Internet Standards]]