Book excerpt: This book details the widely accepted hypothesis that the majority of bacteria in virtually all ecosystems grow in matrix-enclosed biofilms. The author, who first proposed this biofilm hypothesis, uses direct evidence from microscopy and from molecular techniques, arguing cogently for moving beyond conventional culture methods that dominated microbiology in the last century. Bacteria grow predominantly in biofilms in natural, engineered, and pathogenic ecosystems; this book provides a solid basis for the understanding of bacterial processes in environmental, industrial, agricultural, dental and medical microbiology. Using a unique "ecological" perspective, the author explores the commensal and pathogenic colonization of human organ systems.