Transient imaging is a technique in photography that records the process of light propagation before it reaches a stationary state such that events at the light speed level can be observed. In this review we introduce three main models for tran-sient imaging with a time-of-flight (ToF) camera: correlation model, frequency-domain model, and compressive sensing model. Transient imaging applications usually involve resolving the problem of light transport and separating the light rays arriving along different paths. We discuss two of the applications: imaging objects inside scattering media and recovering both the shape and texture of an object around a coer.