Many inheritable changes in gene function are not explained by changes in the DNA sequence. Such epigenetic mechanisms are known to influence gene function in most complex organisms and include effects such as transposon function, chromosome imprinting, yeast mating type switching and telomeric silencing. In recent years, epigenetic effects have become a focus of research activity. This monograph, edited by three biologists from different specialties, reviews and synthesizes what is known about these effects across all species, particularly from a molecular persepctive. It should be of interest to those in the fields of molecular biology and genetics.