Duration: An extended rest is at least 6 hours long.
Once per Day: After a creature finishes an extended rest, it has to wait 12 hours before beginning another one.
No Strenuous Activity: A creature normally sleeps during an extended rest but doesn’t have to. The creature can engage in light activity that doesn’t require much exertion.
Regain Hit Points and Healing Surges: At the end of an extended rest, a creature regains all lost hit points and all spent healing surges.
Regain the Use of Powers: At the end of an extended rest, a creature regains the use of expended encounter powers and daily powers.
Action Points: At the end of an extended rest, a creature loses any unspent action points, but starts fresh with 1 action point.
Interruptions: If anything interrupts a creature’s extended rest, such as an attack, add the time spent dealing with the interruption to the total time the creature needs to spend in the extended rest.
Published in Player's Handbook, page(s) 263, Rules Compendium, page(s) 172.