Polytypic structures often occur in minerals with layer structures. Polytypic structures not only have certain significance in genetic mineralogy but also in mineral material science. The study of polytypic structures is part of the research on mineral crystal structures. Based on previous research (Wang et al. 1982; Pan 1993; Qin 2011) and the research work of the author of this book, the polytypic structures of minerals and their relationship with physical properties are introduced as follows.