The Metastasis Group of the European Organization for Research on Treatment of Cancer (EORTC) held an International Meeting at the Royal Institution in London on April 2lst-23rd, 1980. The subject was "Clinical and Experimental Aspects of Metastasis" and these Proceedings are the record of that Meeting. Almost all of those who presented a paper or a poster have written up their contributions as chapters of the Proceedings and we have made no distinction here between posters and oral communications. The Organizers and Editors owe a considerable debt of gratitude to all the contributors who without exception presented the results of their work in a clear and concise manner that did much to reveal the essence of the complex problems central to current thinking on met astasis. Moreover most manuscripts arrived well within the deadline - a circumstance which in our experience is unusual. Of the large audience who attended the Meeting many had come from the far distant corners of the World and to them as well as to the presenters of papers the Organizers wish to express their deep appreciation."