  A light scalar degree of freedom, as the one possibly responsible for the
accelerated expansion of the Universe, could leave observable traces in the
inspiral gravitational wave signal of binary systems. In order to study these
effects, we extend the effective field theory formalism of Goldberger and
Rothstein to minimal scalar-tensor theories of gravity. This class of models is
still very broad, because the couplings of the scalar to matter are far less
constrained than those a massless spin-2 field. In most of the paper we focus
on conformal couplings. Using the effective field theory approach, we discuss
the emergence of violations of the strong equivalence principle even in models
that exhibit universality of free fall at the microscopic level. Our results on
the conservative dynamics of the binary and its power emitted in gravitational
and scalar radiation agree with those obtained with the standard post-Newtonian
formalism. We also compare them to more recent work. Finally, we discuss the
implications of considering a disformal coupling to matter.
