Improvements in CMOS image sensors have been instrumental in lowering barriers for embedding vision into a broad range of systems. For example, a high degree of system-on-chip integration allows photons to be converted into bits with minimal support circuitry. Low power consumption enables imaging in even small, battery-powered devices. Simple control protocols mean that companies can design camera-based systems without extensive in-house expertise. Meanwhile, the low cost of CMOS sensors is enabling visual perception to become ever more pervasive. In this tutorial, we will introduce the basic operation, types and characteristics of CMOS image sensors; explain how to select the right sensor for your application; and provide practical guidelines for building a camera module by pairing the sensor with suitable optics. We’ll highlight areas demanding of special attention to equip you with an understanding of the common pitfalls in designing imaging systems.