Current theories of planetary evolution predict that infant giant planets have large radii and very low densities before they slowly contract to reach their final size after about several hundred million years. These theoretical expectations have remained untested for a long time, as the detection and characterization of very young planets is extremely challenging due to the intense stellar activity of their host stars. The recent discoveries of young planetary transiting systems, and the advances in the techniques to model stellar activity, have opened the door to the characterisation of these valuable planets, and to place initial constraints on evolutionary models. There are currently 24 known exoplanets younger than 500 Myr with mass and radius measurements, six of them younger than 100 Myr. However, the findings are not always consistent between different groups, which highlights the difficulty of accurately characterising these systems.

In this presentation I will give a brief overview of the recent history of the detection and characterisation of young extrasolar planets, using transit photometry and radial velocities. I will present the current status of the field, the preliminary conclusions that can be extracted from the current population of characterised young exoplanets, and the challenges associated with these works.