This chapter looks at two interrelated aspects of digital circuit troubleshooting, namely troubleshooting and the test equipment. The chapter is divided into two parts: the first part discusses troubleshooting guidelines for a variety of digital devices and circuits; the second part deals with test and measuring equipment. The chapter begins with general guidelines to troubleshooting digital circuits and then moves on to discuss techniques for troubleshooting specific digital building blocks such as logic gates, flip-flops, counters, registers, arithmetic circuits, memory devices and so on. In the second part of the chapter, some of the more commonly used test and measuring equipment is discussed at length. The test instruments covered here are not necessarily ones that are required by a troubleshooter during the course of fault finding. They also include instruments that are the result of advances in digital technology and have a digital-dominated internal hardware. In fact, this constitutes one of the most important areas where digital technology has so strongly manifested itself. Some of these instruments, such as the digital multimeter (DMM), the logic probe and the digital storage oscilloscope (DSO), are the essential tools of any digital circuit troubleshooter. The chapter is adequately illustrated with a large number of case studies related to digital circuit troubleshooting.