Joints in rocks, as distinct from tectonic faults, are fractures that form without "visible" displacement along the fracture plane. They are usually interpreted as tension fractures and analysed mechanically by employing a continuum mechanical theory of this fracture mode. "Rock Joints" deals exclusively with the mechanical genesis of joints in rocks. It is aimed at a coherent, critical and comprehensible presentation of the underlying mechanical processes of various types of joints and joint systems. In addition to tension fractures, the book extensively treats jointing from a different origin, i.e. hydraulic intrusion fractures, cleavage fractures, and shear joints. Throughout, special care is taken to elucidate and quantify the role of high fluid pressures in joint formation. Field examples illustrate formational aspects of jointing, and Mohr's stress circle used where possible to simplify the mathematics.