  We summarize and extend recent work on the theory of extrasolar giant planets
(EGPs) and brown dwarfs, paying particular attention to Gliese 229 B, the
albedos of EGPs, the compositions of substellar atmospheres, the connections
with the giant planets in the solar system, cloud physics, and non-gray
spectral synthesis. The role of condensates in altering the optical spectrum of
Gliese 229 B is explored, as are the systematics of the reflection spectra from
extrasolar giant planets near their primaries. In addition, we discuss the role
of convection and disequilibrium chemistry in explaining the anomalous
detection of CO in Gliese 229 B. Throughout, we highlight the distinctive
chemistry that defines this new class of objects and set goals for future
study.

Astrophysics