The contributions in this volume report recent studies on the sun and late-type stars. Particular emphasis is placed on observations that are relevant to the question of large-scale magnetic activity, and also on the theoretical (dynamo) models for such activity. Experimental papers deal with surface imaging techniques. Explicit computer simulations of hydromagnetic turbulence give insight into the magnetic topology and associated fluid motions, especially near the base of the convection zone. In addition, mean-field dynamo models are presented. The book addresses researchers but should also Äjbe useful for graduate students.