Abstract
Recent developments concerning the theoretical interpretation of the T Tauri phenomenon are briefly summarized: New evolutionary model computations clarified the possibilities and limitations of predicting the basic properties of pre-main sequence stars and their dependence on the initial conditions. Improved computations of the radiative transfer in T Tauri atmospheres and cireunstellar envelopes made it possible to reproduce the major spectral properties of these objects. Other model computations resulted in new insights into the causes and mechanisms of the circumstellar mass flows associated with T Tauri stars. Finally, new mechanisms which may cause the observed strong time variability of pre-main sequence stars have been studied.
