The in situ hybridization and PCR technologies are now well-established molecular techniques for studying chromosomal aneuploidy and rearran- ments, gene localization and expression, and genomic organization. Over the last decade, we have seen increasing applications in these fields. By combining the high sensitivity of the PCR reaction and the cytological localization of target sequences, both PRINS and in situ PCR techniques have provided highly powerful complements to FISH for in situ cellular and molecular investigations. Both these approaches have several advantages in terms of sensitivity and specificity, owing to the use of primers and to the fast kinetics of annealing and elongation reactions in situ. In the first edition of PRINS and In Situ PCR Protocols edited by John R. Gosden, experts in the field presented in detail a variety of applications of PRINS and in situ PCR techniques, in a wide range of clinical conditions. Since the publication of this successful reference book, there have been s- nificant improvements in in situ detection techniques. This completely revised and updated second edition presents a compreh- sive selection of new procedures developed in the field of PRINS and in situ PCR technologies. The book has two sections. Part I, Basic Methodology, contains chapters that provide useful protocols for many variations of PRINS and in situ PCR, including a new fast multicolor PRINS method, and protocols for PRINS detection of unique sequences in situ.