  We present a unified framework for the study of late time cosmic
acceleration. Using methods of effective field theory, we show that existing
proposals for late time acceleration can be subsumed in a single framework,
rather than many compartmentalized theories. We construct the most general
action consistent with symmetry principles, derive the background and
perturbation evolution equations, and demonstrate that for special choices of
our parameters we can reproduce results already existing in the literature.
Lastly, we lay the foundation for future work placing phenomenological
constraints on the parameters of the effective theory. Although in this paper
we focus on late time acceleration, our construction also generalizes the
effective field theory of inflation to the scalar-tensor and multi-field case
for perturbatively constructed backgrounds.
