There is a reasonable survey paper in AIJ in 98. Its 36 pages:
Leslie Pack Kaelbling, Michael L. Littman and Anthony R. Cassandra, Planning and acting in partially observable stochastic domains, Artificial Intelligence, Volume 101, Issues 1-2, May 1998, Pages 99-134.
Also for a shorter introduction see Tony Cassandra’s POMDPs for dummies site:
I wanted to use the first paper at:
But the postscript was getting ugly for me.
Wait for confirmation from Rao, but I think the first paper should be enough, if not, too much.