The theory of General Relativity is probably not the ultimate theory of gravity. This affirmation is motivated by theoretical considerations linked to search to a quantum theory of gravity and to attempt to unify all physical fundamental interactions. Another motivations come from cosmological observations explained by the introduction of Dark Matter and Dark Energy unobserved directly until now. In this thesis, we propose to derive experimentally observable signatures coming from alternative theories of gravity. To reach this goal, we have developed tools to simulate observations in alternative theories of gravity at two different scales: within the Solar System and at cosmological scales. In the Solar System, we have developed software allowing to simulate spatial observations (Range, Doppler and astrometry). At the cosmological level, we have developed software to simulate distance-luminosities observations from Supernova Ia. These tools allow to derive signatures characteristic from alternative theories. We have applied these tools at different alternative theories of gravity to answer to the question: What is the impact due to a modification of the gravitation theory on observations and it is possible to detect these alternative theories ?
