The book "Detection of Low-Level Optical Signals" is aimed at professionals involved in the development of photodetectors and photodetecting systems. It provides comprehensive insights into the challenges and solutions associated with capturing weak optical signals. The authors, led by M. A. Trishenkov, illuminate the critical features of photosensitive devices, particularly their detectivity, which describes the ability to recognize optical signals above the noise level. These characteristics are essential for the performance of optoelectronic systems, including their range, resolution, and precision. The book discusses the development of photodetectors capable of covering various optical wavelength ranges while achieving high quantum efficiency and minimizing noise levels. It is an indispensable work for engineers and scientists working in the fields of IR technologies, optoelectronic systems, and optical communication.