SpaceX to Test Soft-Landing First Stage Post-Mission in Marchby Bruce Perens at Quality:
Lifting a payload into orbit is "astronomically" expensive because the rocket is used up in one flight. Think of what it would cost if you had to buy a new car for every drive you took! That's what we're doing with rockets today.
The Space Shuttle was one approach to solving this problem, but only returned the orbiter, expending its outer tank and solid boosters. Complications of the orbiter made it more expensive than conventional rockets.
SpaceX intends to address this problem by soft-landing the Falcon's two boosters and the Dragon vehicle after use. They've scheduled an over-water propulsive return test of the Falcon 9 first stage as part of March's Space Station Commercial Re-Supply 3 flight (CRS-3). There will probably also be a re-fire of the second stage to initiate controlled re-entry. The extent planned for the second-stage maneuver is unknown at this time.
The first stage may be fitted with carbon-fiber, gas-pressurized landing legs. The first stage landing dynamics have been tested in the many Grasshopper flights. SpaceX will attempt to perform as if soft-landing the first stage, but over water, eventually dropping the booster into the ocean for recovery.
SpaceX first tried the soft-landing maneuver in September, 2013, bringing the first stage close to the ocean's surface in controlled rocket descent before an uncontrolled roll. The second stage was also refired, but this maneuver was aborted due to a transition beyond expected parameters.
This video shows the concept first and second-stage soft-landing.