If dark matter couples directly to a light force mediator it may form bound states in the early universe and in the non-relativistic environment of haloes today. Examples of dark matter bound states are "Wimponium" and the "dark atom". In this talk I will present a field-theoretic framework for the computation of bound-state formation cross-sections and decay rates. At low relative velocities of the interacting particles, the formation of bound states is enhanced by the Sommerfeld effect. We show that bound-state formation can be faster than annihilation into radiation in the regime where the Sommerfeld effect is important.
