This book includes contributions to the International Astrophysics Conference on Mass–Tranfer Induced Activity in Galaxies, held at the University of Kentucky, Lexington, on April 26–30, 1993. More than 140 participants from 17 countries attended, compared to 70 planned originally. We feel that such interest was fueled at least in part by the Conference being solely devoted to this fascinating subject.

This Conference was based on a number of review talks which prepared the audience for the follow-up discussion and contributed papers. We aimed at providing a balanced view of the field which by now has become well defined, reaching a certain degree of maturity. Some overlap between different review papers was planned and the careful reader will enjoy sometimes contradictory explanations of the same ‘facts’.

The main question concerning the origin of active galaxies is tantalizingly simple: how does nature remove all but ∼ 10-7 of the angular momentum (in AGNs) initially residing in the gas a few kpc from the center, accomplishing this on the orbital timescale? And how do the nuclear starbursts fit within this picture — as a passive by-product or a major player forcing the gas inwards and/or outwards?

We proceed from ‘inside out’ (in the footsteps of the Creator?) by addressing first the angular momentum transfer within the central parsec. Next, the kinematics and molecular, atomic and ionized gas distributions in the circumnuclear region are reviewed followed by large-scale gas properties in barred and normal disk galaxies and in ellipticals.