  Modified f(R) gravity is one of the most promising candidates for dark
energy, and even for the unification of the whole cosmological evolution,
including the inflationary phase. Within this class of theories, the so-called
viable modified gravities represent realistic theories that are capable of
reproducing late-time acceleration, and satisfy strong constraints at local
scales, where General Relativity is recovered. The present manuscript deals
with the analysis of the cosmological evolution for some of these models, which
indicates that the evolution may enter into a phantom phase, but the behavior
may be asymptotically stable. Furthermore, the scalar-tensor equivalence of
f(R) gravity is considered, which provides useful information about the
possibility of the occurrence of a future singularity. The so-called Little Rip
and Pseudo-Rip are also studied in the framework of this class of modified
gravities.
