Apoptosis, or programmed cell death, is a common phenomenon which involved in a variety of physiological and pathological conditions in humans, such as neurodegenerative diseases, ischemic injury, autoimmune diseases and cancers. Apoptosis can be detected in vitro by morphology, biochemistry, molecular biology, immunology, and other techniques. Probes for cell apoptosis detection in vivo are still under research and various reagents and methods are constantly emerging. However, none of apoptosis detection methods or reagents are perfect and they all have advantages and disadvantages, as well as suitable scope of application. With the increasing application of apoptosis detection techniques, researchers will be confused about how to choose a suitable method to detect apoptosis and define the application range of each apoptosis detection method. Therefore, it is necessary to compare the benefits and drawbacks of existing apoptosis detection techniques as well as their applicable conditions. This article reviews morphological characteristics, molecular mechanism and specific biochemical changes in apoptotic cells. We summarized various apoptosis-detection methods based on these characteristics that can be used in vitro and in vivo, the advantages and disadvantages of each method and the scope of application. Also, we highlighted the existing tracers that have been used in apoptosis detection in vivo, their potentialities and limitations as well as the clinical applications of apoptosis imaging in multiple disease fields.