This chapter primarily discusses the characteristics of rock engineering and its associated geological environment. It presents the geological elements that influence the engineering properties of rock masses, as well as the basic composition of rocks, their geological origins, and the field identification of the three major rock types. Furthermore, it elaborates on the origins and structural types of rock mass discontinuities, systematically elucidates the fundamental composition, influencing factors, and distribution patterns of in-situ stresses, and briefly outlines methods for measuring and estimating in-situ stresses.