The Kempe change is the essence of the Kempe’s “proof” of the Four Color Conjecture (Kempe, Am. J. Math. 2(3), 193–200 (1879)), by which a new 4-coloring of a maximal planar graph can be generated from a given 4-coloring. The fundamental reason why it fails to prove the Four Color Conjecture by using this technique is that there exist many maximal planar graphs G such that the set of all 4-colorings of G can not be generated by applying Kempe change from any given 4-colorings of G. Nevertheless, due to the NP-completeness of the vertex coloring of graphs, Kempe change has been a fundamental and most powerful tool in the study of theory, algorithm, and application of graph colorings since 1879. This chapter is devoted to the introduction of related theory on Kempe change, including Kempe equivalence of colorings, \(\sigma \) -characteristic graphs (which depicts the relation of all colorings), and non-Kempe graphs.