In recent years several different gene silencing phenomena have been discovered in plants. The term "gene silencing" refers to a partial or complete inactivation of the expression of endogenous genes, transposable elements and, most frequently, transgenes. In contrast to transgene inactivation reported for mammalian systems, gene silencing in plants is not limited to the transgene alone. Insertion of a transgene into the plant genome can also trigger inactivation of homologous endogenous genes. This book summarizes the most recent data on gene silencing phenomena such as transinactivation, paramutation and co-supression. Plant researchers will find this edition a valuable help in differentiating between a number of puzzling and partly contradictory gene silencing events. Readers not familiar with plant molecular biology are introduced into the relevant methods and scientific models. In addition, four review articles, written by leading experts in their field, present examples and models of gene silencing in flamentous fungi, Drosophila and mammalian systems. By providing a comparative update on gene silencing effects in different eukaryotes, this book should stimulate communication among scientists working in diverse areas of eukaryotic gene regulation.