  Bound state perturbation theory is well established for QED atoms. Today the
hyperfine splitting of Positronium is known to $O(\alpha^7\log\alpha)$. Whereas
standard expansions of scattering amplitudes start from free states, bound
states are expanded around eigenstates of the Hamiltonian including a binding
potential. The eigenstate wave functions have all powers of $\alpha$, requiring
a choice in the ordering of the perturbative expansion. Temporal $(A^0=0)$
gauge permits an expansion starting from valence Fock states, bound by their
instantaneous gauge field. This formulation is applicable in any frame and
seems promising even for hadrons in QCD. The $O(\alpha_s^0)$ confining
potential is determined (up to a universal scale) by a homogeneous solution of
Gauss' law.
