The purpose of this survey is to introduce a novel interval observer based fault diagnosis technique. We particularly summarize various interval observers for different systems and discuss design conditions. For example, the event-triggered fault detection method based on interval observers, the parameter-dependent interval observer based fault detection scheme for linear parameter-varying systems, the fault isolation method for T-S fuzzy interconnected systems with unknown interconnections by using interval observers, as well as the interval observer based fault isolation method for discrete-time multi-agent systems. The common goal of discussion on these topics is to highlight the advantages of the interval observer based fault diagnosis schemes. Finally, some open problems in the field are pointed out.