The present work is a continuation of the work initiated in Autumn 1991, which resulted in the book, published by Birkhauser Verlag in 1994, entitled: Methods for Risk Assessment of Transgenic Plants. I. Competition, Establishment and Ecosystem Effects. Already when the work on volume 1 started, it was obvious to the authors, that t only the physical establishment of a transgenic plant outside the cultivated area was important for risk assessment, but also the possible gene-transfer from transgenic plants to other plants had to be considered. It was then decided to write a second volume on test methods, as a complement to the first, covering the main topics: Pollination, gene-transfer and population impacts. The main user groups for this volume are scientists and students working with plant population genetics and risk assessment and administrators with responsibility for legislation of transgenic plants. In order to cover such a broad range of topics, specialist kwledge was required. Therefore, colleagues in Denmark and Switzerland, working in these fields in relation to the concerns of using transgenic plants, were asked to participate. The result was a Danish-Swiss cooperation. A list of contributors to the book and their addresses is shown on p. VII. Financial support, which made the work possible, was given by: The National Environmental Research Institute, Denmark, the Federal Office of Environment, Forest and Landscape, Switzerland, the National Forest and Nature Agency, Denmark, the Danish Environmental Protection Agency and the European Commission, DC XI.