<i>This course presents a unified introductory explanation of electro-optical sensor systems, both passive (IR/VIS/UV) and active (laser radar, ladar). Principles of operation are derived in an analytical approach to enable performance prediction. System components are identified and technology and phenomenology issues are described. Emphasis is placed on (1) the complementary roles of passive and active sensors, (2) the requirements allocation process, and (3) performance of integrated passive and active sensor systems in emerging practical applications.