A bolometer is a device for measuring the energy of incident electromagnetic radiation. It consists of an "absorber" connected to a heat sink through an insulating link. The result is that any radiation absorbed by the absorber raises its temperature above that of the heat sink; then the higher the energy absorbed, the higher the temperature will be. This book gathers and presents current research in the study of bolometers including investigations of properties of high temperature superconducting bolometers, operating uncooled resistive bolometers in a closed-loop mode, as well as a review on thin-film micro-bolometers with Si-Ge thermo-sensing films deposited from plasma discharge.