  Observations with the RXTE and SAX satellites have recently led to the
measurement of a second component in the spectra of several clusters of
galaxies which are known to have regions of extended radio emission. This new
component is quite likely nonthermal emission resulting from Compton scattering
of relativistic electrons by the cosmic microwave background. The nonthermal
X-ray and radio measurements yield the values of the mean intracluster magnetic
field, and relativistic electron density, for the first time in extragalactic
environments. These results have important consequences on issues such as the
origin of cosmic ray electrons and protons, their propagation modes in
clusters, and the effects of these particles and magnetic fields on the
intracluster gas. The observational results are reviewed, and some of their
direct implications are discussed, along with near-future prospects for
improved spectral and spatial measurements of nonthermal emission in clusters.
