This Technical Report gives an overview of biodegradation tests for the aquatic environment standardized by ISO and provides recommendations on their use. In Annex A, the biodegradation guidelines for the aquatic medium of the OECD are included, because these methods are sometimes identical to ISO standards or are useful supplements. In addition, inhibitory tests with bacteria and mixed bacterial inocula are included in this Technical Report because a possible toxicity on the inoculum is important information for the choice and performance of biodegradation tests. It is very helpful to determine bacteria toxicity in advance using the same inoculum as the planned biodegradation test before starting biodegradation testing.