Extrasolar comets, or exocomets, are detected using transit spectroscopy in young planetary systems. In particular, Beta Pictoris observations revealed a high rate of transits, allowing statistical analysis of exocomets populations in this system. With the study of more than 1,000 archive spectra, we obtained a sample of several hundred exocomets signatures in transit in front of Beta Pictoris. The statistical analysis showed the existence of two populations with different physical and dynamic properties. A first family consists of exocomets, which can be attributed to ancient comets trapped in a mean motion resonance with a massive planet, possibly beta-Pic b. The second family consists of exocomets, which may be the result of the recent fragmentation of one massive parent body.

Recently, our observations obtained with the Hubble telescope led to the first detection of exocomets in the far ultraviolet. Several atomic elements have been detected for the first time in these exocometes, in particular atomic hydrogen, oxygen and neutral nitrogen. The measurement of the abundance of these species in the exocomets is crucial to understand the processes of condensation and evaporation present in the last stages of the planetary formation. Preliminary results will be presented.
Finally, we will present analysis of Kepler light curves, that can be interpreted by exocomets transits. Peculiar attention will be given to the case of KIC8462852.