This textbook covers the fundamentals, important individual elements, and systems of optical sensor and measurement technology. The first part deals with the propagation of Gaussian beams, the photoelectric effect, electromagnetic waves, and imaging errors. In the second part, the essential building blocks of optical sensors are introduced, such as LEDs, lasers, photodiodes, and optical fibers. Finally, in the third part, complex systems are described in their function and with application examples, including light barriers, fiber sensors, flow measurement technology, particle measurement technology, and telescopes. The target group is students in technical and scientific courses such as mechatronics, sensor technology, physical engineering, electrical engineering, and mechanical engineering.