Maintenance of the information embedded in the genomic DNA sequence is essential for life. DNA polymerases play pivotal roles in the complex physiological processes of DNA replication and repair. Besides the tasks in vivo, DNA polymerases are the workhorses in numerous biotechniques such as polymerase chain reaction (PCR), cDNA cloning, genome sequencing, nucleic acidsbased diagnostics, as well as techniques to analyze ancient and otherwise damaged DNA. The authors have recently witnessed the discovery of a plethora of novel DNA polymerases with specialized properties whose physiological functions are only just beginning to be understood. This book summarizes the current knowledge of these fascinating enzymes in viruses, bacteria, archaea and eukaryotes. Moreover, some diseases are related to DNA polymerase defects, and chemotherapy through inhibition of DNA polymerases is used to fight HIV, Herpes, as well as Hepatitis B and C infections. This book will appeal to a broad audience including basic scientists, diagnostic laboratories, and clinicians who will gain an invaluable understanding of these fascinating enzymes.