This monograph is a comprehensive survey of the results obtained on the geometry of classical groups over finite fields mainly in the 1960s and early 1990s.For the convenience of the readers I start with the affine geometry and projective geometry over finite fields in Chapters 1 and 2, respectively. Among other things, the affine classification of quadrics is included in Chapter 1, and conics and ovals are studied in detail in Chapter 2. From Chapter 3 and onwards the geometries of symplectic, pseudo-symplectic, unitary, and orthogonal groups are studied in succession. The book ends with two appendices, on the axiomatic projective geometry, and on polar spaces and finite generalized quadrangles, respectively. Now I shall say a few words about the problems we are going to study in Chapters 3-7, and in addition give some historical remarks.