  Radiation reaction (but, more generally, fluctuations and dissipation) occurs
when a system interacts with a heat bath, a particular case being the
interaction of an electron with the radiation field. We have developed a
general theory for the case of a quantum particle in a general potential (but,
in more detail, an oscillator potential) coupled to an arbitrary heat bath at
arbitrary temperature, and in an external time-dependent $c$-number field. The
results may be applied to a large variety of problems in physics but we
concentrate by showing in detail the application to the blackbody radiation
heat bath, giving an exact result for radiation reaction problem which has no
unsatisfactory features such as the runaway solutions associated with the
Abraham-Lorentz theory. In addition, we show how atomic energy and free energy
shifts due to temperature may be calculated. Finally, we give a brief review of
applications to Josephson junctions, quantum statistical mechanics, mesoscopic
physics, quantum information, noise in gravitational wave detectors, Unruh
radiation and the violation of the quantum regression theorem
