Аннотация:A brief overview of the current state of investigation of classical T Tauri and Ae/Be Herbig stars is presented. We describe the application of magnetospheric disk accretion theory to interpretation of activity of these objects. The connection between the accretion and matter outflow from the vicinity of these stars in the form of jets and disk wind is discussed. We also consider the variability of young stars caused by circumstellar dust and the role of episodic accretion in the process of star formation.