"In situ" hybridization is a technique of molecular biology that is used to localize the genetic machinery (genes) involved in protein production, by the use of complimentary strands of genetic material (oligonucleotides of DNA or RNA). It is important in the study of the mechanisms underlying cellular function and disease. This book covers all aspects of "in situ" hybridization, from the basic principles of molecular biology, through the various methodological advances, to its most up-to-date applications in pathology.