As performance-based design methodologies, which typically include use of nonlinear response history analysis, are being used more commonly, comprehensive expressions for nonlinear deformation capacity are needed. Based on a wall test database consisting of conventional reinforced concrete walls representing existing building stock, statistical studies were conducted to assess and develop relations for nonlinear deformation capacity of shear walls depending on expected wall behavior: Deformation capacity was associated with failure modes, which are identified based on experimental evidence, and was defined as failure drift ratio and curvature ductility for shear-controlled (usually squat) walls and flexure-controlled (relatively slender) walls, respectively. Mean drift ratio at failure was obtained as approximately 1% for shear-controlled walls, whereas mean curvature ductility was approximately 4.6 for flexure-controlled walls. Detailed regression analyses were carried out to obtain equations for deformation capacity based on wall failure modes in terms of key wall parameters. The proposed equations are practical, interpretable, and compatible with physical behavior. The proposed equations are valuable in that they can be used by engineers to provide reliable designs by assessing demand-to-capacity ratios, as they were shown to estimate deformation capacity of rectangular walls reasonably close to actual (experimental) values.