Experimental rock deformation the brittle field Introduction. Experimental Procedures. Griffith Theory of Brittle Failure. Evolution of Physical Properties during Brittle Failure. Micromechanics of Brittle Failure. The Role of Pore Fluids. Friction and Sliding Phenomena. Brittle Ductile Transition. Appendix 1 Fracture Mechanisms. Appendix 2 Plasticity Theory and Localization Analysis. Appendix 3 Constitutive Relations for Friction