These proceedings are based on the presentations made during the conference on "Forest Gene Reserves" at a meeting of the Forum Genetik-Wald-Forstwinschaft held in Birmensdorf at the Swiss Federal Research Institute WSL in October, 1998. Nineteen papers address basic and conceptual aspects of the in situ conservation of forest genetic resources, as well as more practical issues. Several contributions deal with relevant activities at the national, regional, and international levels. Criteria for the selection of in situ gene reserves are discussed in detail. Of particular urgency are measures for the conservation of the genetic resources of rare species. Numerous examples, some of which are based on previously unpublished data, are used to illustrate the importance of taking into account the special features of the genetic system of target species when implementing effective protection measures. The conservation of genetic resources in in situ gene reserves will continue to play a central role in the conservation of forest trees, although in many cases further complementary measures will be necessary.