Analog and mixed-signal (AMS) circuits are becoming more critical in the system on- chip (SOC) era, although they are occupying less silicon area. AMS circuits are designed using specialized techniques because a wide range of circuit structures are possible. This chapter introduces AMS circuits, failure modes, and fault models. It then addresses analog testing, including DC and AC parametric testing. Waveform-oriented testing and specification-oriented testing are reviewed in the chapter. Then, mixed-signal circuits, analog-to-digital converters (ADCs), digital-to-analog converters (DACs), and their testing approaches, are discussed. This chapter also illustrates that, terminology and test approaches are consistent with the IEEE 1057 standard. Finally, the IEEE 1149.4 standard for mixed-signal test buses is studied. Two analog test buses are employed to deliver test stimuli and test responses in board-level analog interconnect testing and passive component measurement.