Recent cosmological data predict an actual acceleration of the
universe. This opens up the possibility that general relativity is
modified at very large distances, given typically by the inverse Hubble
scale. We will discuss the possible explanations to late-time
acceleration, in particular that of a tiny cosmological constant and dark
energy models, their major advantages and drawbacks. Then we will examine
modified gravity theories, their main characteristics, their theoretical
and experimental setbacks. We will end our discussion with maybe the most
well-known, consistent and simple modification, Brans-Dicke theory and
question whether higher order gravity corrections can modify usual very
restrictive solar system constraints.