http://www.alpa.org/portals/alpa/1500Rule/

The short version
"Beginning Aug. 1, 2013, to be a copilot for a U.S. FAR Part 121 airline, you’ll have to hold an ATP or a “restricted” ATP certificate. All airline pilots may have to hold a first class airman medical certificate (but ALPA has filed a Petition for Exemption with the FAA to allow first officers to continue to fly on a second class airman medical certificate).

First officers also will be type-rated in the aircraft they intend to fly in FAR Part 121 service. "

http://www.alpa.org/portals/alpa/1500Rule/FinalRule.pdf

(Airlines have until 2016 to type existing employees)