  Emission from astronomical jets extend over the entire spectral band: from
radio to the TeV gamma-rays. This implies that various radiative processes are
taking place in different regions along jets. Understanding the origin of the
emission is crucial in understanding the physical conditions inside jets, as
well as basic physical questions such as jet launching mechanism, particle
acceleration and jet composition. In this chapter I discuss various radiative
mechanisms, focusing on jets in active galactic nuclei (AGN) and X-ray binaries
(XRB) environment. I discuss various models in use in interpreting the data,
and the insights they provide.
