With climate change and the increment of human activities, global permafrost is undergoing degradation, threatening the stability of engineering and the ecological environment of the permafrost region. With the advantages of all-day, all-weather, wide-coverage, and high-accuracy monitoring, synthetic aperture radar interferometry (InSAR) is becoming a substantial tool for permafrost monitoring, and many studies with InSAR in permafrost regions have been conducted in the recent 20 years. In this article, the basic principles of time–series InSAR are introduced first. Then, the development and applications of InSAR in permafrost, such as the coherence analysis of permafrost ground surface, the deformation of permafrost and infrastructure, and active layer thickness (ALT) retrieval, are given. Next, the existing problems, including temporal decorrelation, atmospheric delay, deformation models, and the effect of soil moisture and phase unwrapping (PU), are discussed.