I can't seem to find any official documentation on this, so here are my notes. Some information gathered from http://richmarr.wordpress.com/tag/calendar/ Other information gathered through trial and error, and close examination of the "Add Event" form on Yahoo!'s site. Yahoo! Calendar URL Parameters Parameter Required Example Value Notes v Required 60 Must be 60 . Possibly a version number? TITLE Required Event title Line feeds will appear in the confirmation screen, but will not be saved. May not contain HTML. ST Required 20090514T180000Z Event start time in UTC. Will be converted to the user's time zone. 20090514T180000 Event start time in user's local time 20090514 Event start time for an all day event. DUR value is ignored if this form is used. DUR 0200 Duration of the event. Format is HHMM, zero-padded. MM may range up to 99, and is converted into hours appropriately. HH values over 24 hours appear to be modulated by 24. Durations t...