Experimental Evidence and Elementary Theory -- Hydraulic Fractures -- Termination and Spacing of Tension Joints in Layered Rocks -- Multiple Sets of Tension Joints -- Shear Joints -- Joints in Faulting and Folding -- Échelon Joints and Veins. 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. Special care is taken to elucidate and quantify the role of high fluid pressures in the formation of joints. The background is an offshoot of the author's courses on "Genesis of Rock Joints" in the Department of Rock Mechanics and Tunneling at the Technical University of Graz, Austria.