In order to allow a reproducibly assessment of potential effects of pollutants a standardisation of ecotoxicity tests is necessary. While a range of standardised tests on environmental impacts of pollutants is available, their implementation in nano-toxicity testing is difficult and many of those methods are unsuitable for assessment of engineered nanomaterials (ENM). Small changes in environmental parameters or testing procedures can change the physico-chemical characteristics of the tested ENM and thereby influence the study results. In order establish guidelines and standard procedures for ecotoxicological assessment of ENMs, the NanoReg project aims to test, optimise and validate a set of suitable test methods for different types of ENMs. Preparation and characterisation procedures, a prerequisite for ENM toxicity evaluation, were established and validated for different ENMs in laboratories across Europe. Further, standard tests for toxicological assessments using the freshwater aquatic species Pseudokirchneriella subcapitata and Daphnia magna were evaluated and adapted to suit needs for ENM testing. A wide range of ENMs from various material classes are tested for their environmental stability and their potential ecotoxicological effects using the adapted ENM-standardised methods. The tested materials include different carbon based ENMs (native and modified single- and multi-walled carbon nanotubes, graphene and graphene oxide); a range of modified and unmodified titanium dioxide (TiO2) based ENM, as well as metal ENMs. This large scale testing with suitable standardised methods will provide valuable ecotoxicological data and further show if a read across or grouping approach of similar ENMs is possible. Similarities between ENMs such as size, material and surface for potential read across or grouping approaches in aquatic toxicity tests can be identified.