  We construct an effective field theory valid for processes in which highly
energetic light-like particles interact with collinear and soft degrees of
freedom, using the decay B -> X_s + gamma near the endpoint of the photon
spectrum, x = 2 E_gamma / m_b -> 1, as an example. Below the scale mu=m_b both
soft and collinear degrees of freedom are included in the effective theory,
while below the scale mu=m_b sqrt{x-y}, where 1-y is the lightcone momentum
fraction of the b quark in the B meson, we match onto a theory of bilocal
operators. We show that at one loop large logarithms cancel in the matching
conditions, and that we recover the well known renormalization group equations
that sum leading Sudakov logarithms.
