CalConnect recently published a Starter List of CalDAV and CardDAV Standards and Specifications, a list of specifications and protocols recommended to people getting started with developing a CalDAV and/or CardDAV server but not yet fully conversant with the specs. The list is divided by major topic (HTTP, CalDAV, etc.) and each spec is identified by a short description indicating what it is and what it is used for in this context.
We are planning to publish a comprehensive CalDAV and CardDAV Protocol Reference List in the near future as a complement to this Getting Started list; the Index to Calendaring and Scheduling Standards may also be of use.
Note: The page was originally called “Getting Started with CalDAV and CardDAV” but we changed the name to more accurately reflect the content. The old Getting Started link is aliased to the Starter List page.