  X-ray observations of Young Stellar Objects (YSOs) have shown several complex
phenomena at work.In recent years a few X-ray programs based on long,
continuous and, sporadically, simultaneous coordinated multi-wavelengths
observations have paved the way to our current understanding of the physical
processes at work, that very likely regulates the interaction between the star
and its circumstellar disk. We will present and discuss some recent results
based on a novel analysis of few selected very large flares observed with the
Chandra Orion Ultradeep Pointing (COUP), on the systematic analysis of a large
collection of flares observed with the Coordinated Synoptic Investigation of
NGC 2264 (CSI 2264) as well as on the Class I/II YSO Elias 29, in the rho Oph
star forming region, whose data have been recently gathered as part of a joint
simultaneous XMM-Newton and NuSTAR large program.
