Bound-state wave functions and bound-state scattering in relativistic field theory

We describe how a matrix element of an operator may be calculated between bound states, in the framework of conventional relativistic field theory. In the course of doing so, we examine how bound-state creation and annihilation operators may be constructed, the asymptotic condition for bound states, what general types of wave functions are appropriate for describing bound states and why, graphical analysis involving bound states, and questions of renormalizability. The final result is a set of Feynman-type rules for calculating a matrix element. Those for the $S$ matrix are stated explicitly.