  Bound states are stationary in time and interact continuously. Even a first
approximation of atomic wave functions in QED requires contributions of all
orders in \alpha. Bound state perturbation theory depends on the choice of this
first approximation, just as the Taylor expansion of an ordinary function
depends on the expansion point. Considering the expansion to be not in $\alpha$
but in $\hbar$, i.e., in the number of loops, defines the perturbative
expansion uniquely also for bound states. I show how the Schr\"odinger equation
for Positronium with the classical potential $V(r)=-\alpha/r$ corresponds to
the Born, $O(\hbar^0)$ bound state approximation in QED.
  Standard perturbation theory is based on an expansion around $O(\alpha^0)$
free states that have no overlap with bound states. Perturbing around bound
states requires using interacting $in$ and $out$ states. For Born states the
binding potential arises from a classical gauge field. In the absence of loops
the QCD scale $\Lambda_{QCD}$ can originate from a boundary condition imposed
on the solution of the classical gluon field equations. A perturbative
expansion may be relevant even for hadrons, if their non-perturbative features
such as confinement and chiral symmetry breaking are present already in the
Born term.
