Often, deflection is as important as stress in determining the acceptability of a design, and machine components are often sized in order to achieve acceptable deflections. This chapter presents a number of important approaches for calculating the deflection of beams and other structures. The topics discussed in Chapters 2 though 4 are built upon to demonstrate the methods used to calculate deflection of beams, using both direct integration of moment diagrams or using singularity functions. When complicated loadings exist on a body that encounters small strains (i.e., a linear elastic situation), the method of superposition is a powerful approach to calculate the deflection of the body by considering all loads in tractable combinations. Strain energy approaches, including Castigliano’s Theorem, are then presented. These approaches are especially valuable for impact or energy loadings.