This review by P. L. Richards provides an in-depth look at bolometric detectors for infrared and millimeter waves. It begins with a historical overview, explaining how bolometers fit into the broader category of thermal detectors and their applications. The review then delves into the fundamental theories of bolometer response, thermal radiation, and noise, providing rigorous derivations from thermal physics. Key components of efficient bolometers, such as semiconductor thermometers, composite bolometers, and monolithic silicon bolometers, are discussed, along with their fabrication and performance. The trade-offs involved in using superconducting thermometers at low temperatures are also explored. The review concludes with a discussion of bolometers operating at liquid nitrogen temperatures using high-$T_c$ superconductors and a summary of the challenges and future directions in bolometric radiation detection.This review by P. L. Richards provides an in-depth look at bolometric detectors for infrared and millimeter waves. It begins with a historical overview, explaining how bolometers fit into the broader category of thermal detectors and their applications. The review then delves into the fundamental theories of bolometer response, thermal radiation, and noise, providing rigorous derivations from thermal physics. Key components of efficient bolometers, such as semiconductor thermometers, composite bolometers, and monolithic silicon bolometers, are discussed, along with their fabrication and performance. The trade-offs involved in using superconducting thermometers at low temperatures are also explored. The review concludes with a discussion of bolometers operating at liquid nitrogen temperatures using high-$T_c$ superconductors and a summary of the challenges and future directions in bolometric radiation detection.