  We present a general framework for analyzing fractionalized, time reversal
invariant electronic insulators in two dimensions. The framework applies to all
insulators whose quasiparticles have abelian braiding statistics. First, we
construct the most general Chern-Simons theories that can describe these
states. We then derive a criterion for when these systems have protected
gapless edge modes -- that is, edge modes that cannot be gapped out without
breaking time reversal or charge conservation symmetry. The systems with
protected edge modes can be regarded as fractionalized analogues of topological
insulators. We show that previous examples of 2D fractional topological
insulators are special cases of this general construction. As part of our
derivation, we define the concept of "local Kramers degeneracy" and prove a
local version of Kramers theorem.
