Relativistic Bound States

In this contribution, I will give a brief survey of present techniques to treat the bound state problem in relativistic quantum field theories. In particular, I will discuss the Bethe-Salpeter equation, various quasi-potential equations, the Feynman-Schwinger representation, and similarity transformation methods for Hamiltonian approaches in light-front quantization. Finally, I will comment on a related similarity transformation in the usual equal-time quantized theory.