  Full sky maps are made in five microwave frequency bands to separate the
temperature anisotropy of the CMB from foreground emission. We define masks
that excise regions of high foreground emission. The effectiveness of template
fits to remove foreground emission from the WMAP data is examined. These
efforts result in a CMB map with minimal contamination and a demonstration that
the WMAP CMB power spectrum is insensitive to residual foreground emission. We
construct a model of the Galactic emission components. We find that the Milky
Way resembles other normal spiral galaxies between 408 MHz and 23 GHz, with a
synchrotron spectral index that is flattest (beta ~ -2.5) near star-forming
regions, especially in the plane, and steepest (beta ~ -3) in the halo. The
significant synchrotron index steepening out of the plane suggests a diffusion
process in which the halo electrons are trapped in the Galactic potential long
enough to suffer synchrotron and inverse Compton energy losses and hence a
spectral steepening. The synchrotron index is steeper in the WMAP bands than in
lower frequency radio surveys, with a spectral break near 20 GHz to beta < -3.
The modeled thermal dust spectral index is also steep in the WMAP bands, with
beta ~ 2.2. Microwave and H alpha measurements of the ionized gas agree.
Spinning dust emission is limited to < ~5% of the Ka-band foreground emission.
A catalog of 208 point sources is presented. Derived source counts suggest a
contribution to the anisotropy power from unresolved sources of (15.0 +- 1.4)
10^{-3} microK^2 sr at Q-band and negligible levels at V-band and W-band.
