This book is concerned with new applications of molecular biology techniques to aquatic microbiology and demonstrates the potential to solve some intractable problems. It deals in depth with topics ranging from the ability of molecular techniques to characterize assemblages of microorganisms which cannot be cultured, to novel ways to measure rates of production. In addition to the chapters which emphasize the molecular approach, a number of contributions, written by eminent aquatic microbiologists, highlight important processes that are making rapid progress.