It is well known that extrasolar planets are not where we imagined. Current planetary formation theories, based on planetesimal accretion and core-instability for giant planets, predict bodies in quasi-circular orbits and semimajor axes a far from the star. However, many exoplanets do not follow this rule and are found in highly eccentric orbits and/or a < 1 AU.

Two options have been proposed to explain this dilemma. In the first, it is assumed that present cosmogonic theories are completely wrong, or followed a different route in many other planetary systems, thus making our own Solar System a rather particular case. In the second, exoplanets really did form far from the central star, but suffered a posterior decay in their semimajor axes towards their present sites. This is the so-called "Hypothesis of Planetary Migration". However, in order for migration to be a real option, two conditions must be met: (i) the existence of a plausible driving mechanism to explain the present peculiar orbits, and (ii) concrete evidence that exoplanets did undergo such an evolution.

The aim of this talk is to address several aspects of this problem, and present both difficulties and possible answers to these questions. Beginning with a discussion of different migration scenarios, we shall then analyse the orbital evolution of planetary bodies in this environment, including the phenomena of resonance capture. In a second part, we will study the existence of equilibrium solutions for the 2/1 and 3/1 mean-motion resonances, particularly the cases of aligned, anti-aligned and asymmetric corotations. Finally, a comparison will be presented between the orbital fits of real planetary systems and expected post-migration configurations. These results allow us to "test" the migration scenario and obtain information about the required properties of the driving mechanism.