Since the first published description of a genetically modified (GM) poplar by Fillatti and co-workers1 in 1987, the environmental release of GM trees has spurred public debate worldwide, particularly in the context of commercialization. Although the issues raised in public discussion are similar in many countries, marked political differences have emerged in various countries as to the acceptability of field applications of GM trees, the amount of public funding devoted to GM tree research and the regulatory priorities regarding biosafety issues. Consequently, a large but diverse and fragmented body of knowledge on the environmental interactions and safety of transgenic trees and other (transgenic) organisms has been acquired over the past 25 years.