Book excerpt: Freshwater field tests are an integral part of the process of hazard assessment of pesticides and other chemicals in the environment. This book brings together international experts on microcosms and mesocosms for a critical appraisal of theory and practice on the subject of freshwater field tests for hazard assessment. It is an authoritative and comprehensive summary of knowledge about freshwater field tests, with particular emphasis on their optimization for scientific and regulatory purposes. This valuable reference covers both lotic and lentic outdoor systems and addresses the choice of endpoints and test methodology. Instructive case histories show how to extrapolate test results to the real world.