Book excerpt: Biological Assessment and Criteria presents a state-of-the-art overview of the applications of biological assessments and biocriteria for water quality management in fresh waters. The book presents case studies which illustrate how bioassessment has been used to identify and diagnose water quality problems. It also provides examples of the use of qualitative and quantitative biocriteria as regulatory tools to complement water quality criteria and standards. The first book to present the technical foundation, rationale, program and policy relevance, and legal basis for the most accurate tools used to assess freshwater natural resource and regulatory efforts, this book provides useful and timely information for water quality managers.