Gene silencing is a general term describing the epigenetic processes of gene regulation. The term gene silencing is generally used to describe the "switching off" of a gene by a mechanism other than genetic modification. This book reviews research in the study of gene silencing including RNA silencing in transgenic plants and mycorrhizal research, gene silencing in the CNS and on the most extensively studied systems to mediate siRNA and shRNA delivery into the brain, siRNA delivery strategies as a therapeutic tool in gene therapy, galectin-3 epigenetics and effective methods for selecting siRNA sequences by using the average silencing probability and a hidden Markov model.