Structural characteristics of the rock mass and the strength and fracture properties of its ingredient rocks are important to know as a basis for understanding the blasting process. The chapter introduces some selected areas of rock mechanics and geological engineering, and presents the way the rock materials and rock masses may react to the forces released by the detonation of explosive charges in drillholes. A rock mass, as distinguished from a rock strength test specimen, is a body of rock with its naturally occurring network of flaws and discontinuities, cracks, joints, and planes of weakness. The strength properties of rock when confined and stressed in different directions simultaneously have a profound importance on the understanding of the whole technology of rock fragmentation in drilling, boring, and blasting.