Geomechanics is concerned with the elastic and/or poroelastic response of earth materials, typically in a scientific or engineering setting that involves fluids such as water or oil stored in earth reservoirs. The main issues to be resolved are usually how much water or oil are currently stored in a certain reservoir, or how much fluid (such as carbon-dioxide in its liquid state) or gas can be stored at pressure over long times in a given geomechanical reservoir. Techniques used to study these issues include both numerical methods, involving large finite element or finite difference codes for specific reservoirs, or analytical methods, for understanding general principles and predicting what types of behaviors can be expected over a wide range of field conditions. Geomechanical studies are often coupled to seismic studies of earth reservoirs, and occasionally to other types of geophysical studies, such as electromagnetics, gravity, borehole and logging methods. The range of topics covered includes fluid transport properties, rock-formation fracturing, fault slip resulting from fluid injection or withdrawal, as well as related effects due to thermal loading.