Before defining rigid-body replacement as a way to synthesize compliant mechanisms,let us first reiterate a few basic definitions already established in other parts of thishandbook. Mechanisms are mechanical devices used to transfer or transform motion,force, and/or energy [1]. Linkages are some of the most common types of mechanisms.Rigid-body mechanisms have rigid links and movable joints. These movablejoints are typically pin joints and slider joints. In contrast to rigid-body mechanisms,compliant mechanisms have at least one flexible link or one flexible joint. The pseudorigid-body model (PRBM) is a practical and convenient way to predict the kinematicperformance of compliant mechanisms using traditional rigid-body mechanism analysis.The PRBM is presented in Chapter 5 of this handbook.