We generalize the approach first proposed by Manton [Nucl. Phys. B 150, 397 (1979)] to compute solitary wave interactions in translationally invariant, dispersive equations that support such localized solutions. The approach is illustrated using as examples solitons in the Korteweg–de Vries equation, standing waves in the nonlinear Schrödinger equation, and kinks as well as breathers of the sine-Gordon equation.