  We introduce a hierarchy of closed equations for charge density correlation
functions in the Hubbard model and $2 + 1$ dimensional QED. Each step in the
hierarchy can be considered a large $N$ truncation of an exact, but infinite
set of equations relating all $k-$point charge correlators. $N$ is the number
of fermion spin components. Each step in the hierarchy sums up an infinite
number of large $N$ diagrams, including all diagrams up to some fixed order,
for $k$ point functions with $k \leq K$. Higher point functions are replaced
with their leading large $N$ behavior. The simplest truncation gives a closed
nonlinear equation for the $2$ point function.
