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.Comment: 9 pages, LaTeX, 3 pspicture diagrams, 3 postscript figures, uses
aipxfm.sty. Talk delivered at the X Mexican School of Particles and Fields,
Playa del Carmen, Mexico, 200