Freshwater mussels of the Order Unionida are one of the most imperiled groups of animals, and environmental contamination is often linked as a contributing factor to their decline. However, before the standarization of toxicity test methods in the early 2000s, mussels were generally under-represented in the toxicity databases used for the development of environmental guidance values. In 2006, ASTM International published a standard for conducting laboratory toxicity tests with freshwater mussels. Since, there have been more studies conducted on the propagation and culture of mussels as test organisms, the appropriate life stages for toxicity testing, as well as test duration, feeding and toxicity endpoints. In addition, new test methods have been developed for estimating sediment and effluent toxicity to juvenile mussels. These recent findings and newly developed methods were included in the 2020 revision of ASTM standard method for measuring the toxicity of sediment-associated contaminants with freshwater invertebrates and the 2022 revision of the ASTM standard method for toxicity tests with freshwater mussels. This webinar will provide an introduction to mussels, including taxonomy and distribution, life stages, and laboratory culture, and will illustrate standard test methods and applications, including procedures, equipment, and the use of mussel data in water and sediment quality management.