Android 4.2 (Jelly Bean) SDK platform with API level 17 is available now. get started developing and testing, download the Android 4.2 Platform from the Android SDK Manager.
For a complete overview of what's new, take a look at the Android 4.2 platform highlights or read more of the details in the API overview.
Source: Android Developers Blog - Introducing Android 4.2, A New and Improved Jelly Bean.
