  Modified gravity is one of the most promising candidates for explaining the
current accelerating expansion of the Universe, and even its unification with
the inflationary epoch. Nevertheless, the wide range of models capable to
explain the phenomena of dark energy, imposes that current research focuses on
a more precise study of the possible effects of modified gravity may have on
both cosmological and local levels. In this paper, we focus on the analysis of
a type of modified gravity, the so-called f(R,G) gravity and we perform a deep
analysis on the stability of important cosmological solutions. This not only
can help to constrain the form of the gravitational action, but also facilitate
a better understanding of the behavior of the perturbations in this class of
higher order theories of gravity, which will lead to a more precise analysis of
the full spectrum of cosmological perturbations in future.
