Planescape is boundless. It's a campaign setting whose only limits are those of your own imagination. Not only that, but the rules in all other settings are broken. Old rivalries and enmities are tossed aside. The mundane freely mixes with the strange and surreal. Where else can you find rogue modrons on the run, angels sitting down to tea with devils, or humans hanging out with those who might be called monsters elsewhere?
Such a diverse and boundless setting deserves new player options, ones that reflect the nature of Sigil, the gate-towns, and the worlds beyond. Ones that fire players' imaginations and help them embrace the multiverse. Ones that bring a whole new sphere of play to your fingertips. You're not in the Forgotten Realms anymore, berk!
- from the publisher's blurb