Young stars form by contraction from large molecular clouds, they accrete mass from their environment. In the stage of classical T Tauri stars (CTTS) they are surrounded by an accretion disk, in which planet formation takes place. At this time, there are three possible mechanisms to power X-ray and UV emission: First, a corona similar to main-sequence stars, second, an accretion shock when infalling matter from the disk hits the star and, third, wind and collimated jets.
I will present X-ray and UV observations, that tell us about the physical conditions in the emission regions and show that all three mechanisms can be observed, albeit to a different degree in different objects.