2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/127841Several aspects concerning the origin of the very strong X-ray activity of T Tauri Stars (TTS) are still not well understood. Important new insight came recently from the Chandra Orion Ultradeep Project (COUP), a unique 10-day long Chandra observation of the Orion Nebula Cluster, and the XMM-Newton Extended Survey of the Taurus Molecular Cloud (XEST). Based mainly on the results of these two large projects, I will discuss our current knowledge about the location of the X-ray emitting structures in TTS, the nature of their coronal magnetic fields, inferences for pre-main-sequence magnetic dynamos, and the relation between accretion processes and X-ray emission.Review talk at the Conference "Coronae of Stars and Accretion Disks", Bonn, Germany, December 2006. Conference proceedings to be published in Memorie della Societa Astronomica ItalianaAstrophysicstext