This paper presents a classification of the processes of slow electron emission in solids when excited and stimulated in different ways. All these processes belong to the so‐called exoelectron emission (EEE). We examine phenomenological theories which explain the basic experimental evidence of the non‐stationary thermoemission (TEE). The EEE is described in terms of a kinetic theory close to luminescence theory. The experimental criteria suggested for distinguishing different types of exoelectron emission mechanisms can be used for any broad‐band emitters.