The NIRCam science objectives are the detection and identification of "first light" objects, the study of star and brown dwarf formation, and the detection and characterization of planetary systems and their formation. These three science programs are also the key objectives of the JWST program as a whole. The NIRCam instrument design is optimized for these objectives within the mission constraints. NIRCam consists of two optics modules, each with a field of view of 2.2 arcmin square. The modules are identical except for the mechanical layout. Each module consists of two channels divided by a dichroic beamsplitter. The short wavelength channel has a band pass of 0.6 - 2.3 microns, with pixels sized for Nyquist sampling of the PSF at 2.0 microns. The long wavelength channel has a band pass of 2.4 - 5.0 microns, with pixels sized for Nyquist sampling at 4.0 microns. Selections of wide (R~4), intermediate (R~10), and narrow (R~100) bandwidth filters are provided in each of the four channels, along with coronagraphic occulting masks and pupil stops. A refractive optical design results in a smaller instrument volume and mass, provides good images at the pupils for wavefront sensing and coronagraphy, allows good access to the pupils and focal planes, and relaxes the alignment requirements compared to a reflective design. The NIRCam instrument is funded by NASA/GSFC under contract NAS5-02105.