Production from unconventional reservoirs requires hydraulic fracturing and stimulation of pre-existing faults in order to access more reservoir surface area. Diffusion of fluid pressure from hydraulic fractures induces shear slip on faults by lowering the effective normal stress (Chapter 10). Induced fault slip increases formation permeability through inelastic damage in the surrounding rock and creates a network of relative permeability flow paths that increase access to the ultra-low permeability rock matrix. Slip on pre-existing faults is documented as microseismic events that cluster around hydraulic fractures and are thought to define the stimulated rock volume from which hydrocarbons are produced (Chapter 12). While this paradigm is widely accepted, multiple lines of evidence indicate that the deformation associated with microseismicity can only account for a fraction of production. To understand the relationship between hydraulic stimulation and production, it is important to consider under what conditions faults will slip and whether or not fault slip will cause microseismic events.