Abstract
In this review, the problem of stellar activity is examined into an evolutionary context. A brief description is given of observations related to activity in late-type main sequence stars and of the most likely origen for this activity, namely magnetic field strength and surface coverage. The activity observed in T Tauri stars is then considered, and it is shown that it can be explained with a model which is consistent with that appropriate for more evolved stars. These arguments and recent theoretical developments are then tied together to present an evolutionary picture in which the agent for the activity, the magnetic field, and its result, stellar activity, arise as a natural consequence of the collapse of an interstellar cloud and change with time as the star evolves to end up at the low levels observed in main-sequence stars. In picture, T Tauri Stars constitute the natural link between the interstellar medium and mature stars.
