The collections API have been probably the most frequently requested,
"coming soon" feature that we didn't have a good excuse not to have for
as long as any of us can remember.

There was a hope that we'd get a chance to rewrite collections at some
point, and put these APIs on firmer ground. But it ain't going to
happen before you and I get old.

So I'm going to start rolling out our existing, developed for internal
use APIs, and we're going to see how that goes. Expect breakage, and
feedback is expected.

The first two APIs are the collections getList()/getInfo() style methods
(something you might have noticed we have for nearly every "object" in
the system)

In the case of collections, the method is actually getTree(), as
collections are arranged into nested sets of sets and other collections.

getInfo() pretty much does what it says on the box.

http://www.flickr.com/services/api/flickr.collections.getTree.html
http://www.flickr.com/services/api/flickr.collections.getInfo.html

Good luck, and remember these are experimental for the time being.

Editing methods will be coming down the pipe.

-kellan