  We review the current status of experimental data for spectral distortions
and angular anisotropies of the cosmic microwave background, as well as
discussing the relevant physical processes. This is one of a number of new
articles in astrophysics and cosmology which will appear in the 1996 Review of
Particle Properties (Phys. Rev. D. in press). Other relevant reviews include:
"Big-Bang Cosmology" by K.A. Olive; "Big-Bang Nucleosynthesis" by K.A. Olive &
D.N. Schramm; "The Hubble Constant" by C.J. Hogan; "Dark Matter" by M.
Srednicki; "Cosmic Rays" by T.K. Gaisser & T. Stanev; "Solar Neutrinos" by K.
Nakamura. Additional information is also available, such as astrophysical and
cosmological constraints on particles such as axions and neutrinos, as well as
tables of physical constants and astrophysical constants. These articles are
part of a new initiative to widen the scope of the RPP by providing a regular
review of some important topics and parameters in astrophysics.
