The success of the two first Alexander von Humboldt Colloquia on Celestial Mechanics (March 1984 and March 1988) encouraged us to meet again this year from March 29 to April 4, 1992 in the " Alpengasthof Peter Rosegger"" in the Styrian Alps (Ramsau, Austria). This time the colloquium was devoted to the "Qualitative and Quantitative behaviour of Planetary Systems." The papers covered a large range of questions of current interest from the behaviour of dust particles to the stability of the Solar System as a whole, without forgetting the motion of Asteroids and their classification into families. KAM theory, chaotic motions, resonances, Lyapunov characteristic exponents, perturbation theory, numerical integration were - of course - on the menu every day, served with sauces and accents from various part of the world: from China, from Brazil, from the United States and from all over Europe. To be able to organize this - now well established - meeting, we have to thank primarily the munificence of the Austrian Ministry of Science, furthermore the Steiermarkischen Wissenschafts- und Landesfonds and the Osterreichische Nationalbank for financial support. Also, the Osterreichische Forschungsgemein schaft and the University of Vienna made it possible to invite participants to this meeting from abroad. Support in form of "Tagungsunterlagen" was given by the Creditanstalt-Bankverein in Vienna and coffee during the whole meeting time was donated by Homig-Kaffee Graz."