On July 10, 2008, NASA formally approved the JWST project to move into its implementation phase. This decision followed a successful Preliminary Design Review (PDR) in March 2008 and a Non-Advocate Review in April. While all the science instruments and the "long lead" items like the primary mirror segments are already being manufactured, this approval marks the transition of the program into "Phase C" (Final Design and Fabrication). Phase D covers system assembly, integration and testing and launch. Since portions of this work occur while other subsystems are still in fabrication, NASA aficionados refer to this entire period as Phase C/D. Operations (Phase E: the fun part!) begins after instrument checkout and the cruise to L2.
As of early 2011, eleven of JWST's 18 primary flight segments have completed final polishing. Nine of these segments, as well as the FSM and tertiary have been gold coated and meet spec. The flight instruments will begin delivery to GSFC for integration into the ISIM structure in 2011.
The four instruments - NIRCam, MIRI, NIRSpec, NIRISS and the FGS use advanced detector technologies specifically developed for JWST. Teledyn (formerly Rockwell Scientific) is producing near-infrared HgCdTe detectors for NIRCam, NIRSpec, NIRISS and the FGS. Raytheon is developing mid-infrared Si:As detectors for MIRI under the oversight of the Ames Research Center.
The members of the JWST Science Working Group (SWG) are listed at the SWG pages. The SWG provides guidance on the science goals and capabilities of JWST.
Please follow the Project History link if you want more detailed information on the history of the conception and development of JWST.