  Compton telescopes rely on the dominant interaction mechanism in the MeV
gamma-ray energy range: Compton scattering. By precisely recording the position
and energy of multiple Compton scatter interactions in a detector volume, a
photon's original direction and energy can be recovered. These powerful survey
instruments can have wide fields of view, good spectroscopy, and polarization
capabilities, and can address many of the open science questions in the MeV
range, and in particular, from multimessenger astrophysics. The first
space-based Compton telescope was launched in 1991 and progress in the field
continues with advancements in detector technology. This chapter will give an
overview of the physics of Compton scattering and the basic principles of
operation of Compton telescopes; electron tracking and polarization
capabilities will be discussed. A brief introduction to Compton event
reconstruction and imaging reconstruction is given. The point spread function
for Compton telescopes and standard performance parameters are described, and
notable instrument designs are introduced.
