This Technical Report provides a compilation and description of in vitro and in vivo methods that can be useful for the toxicological, including ecotoxicological screening of engineered and manufactured nanomaterials. Toxicological screening tests included in this Technical Report can be used for such purposes as early decision-making in research and product development, rapid feedback on potential toxicological/safety concerns, or for the preliminary assessment of manufactured nanomaterials. This Technical Report is divided between screening assays related to humans and screening assays related to the environment. A screening test is a relatively simple, inexpensive test that can be administered easily and provides an indication of potential adverse outcomes and effects on human health or the environment. The Technical Report is intended to complement other international efforts that address nanomaterial toxicology by focusing on screening methods suited for preliminary assessment and is not intended to duplicate similar efforts in other international organizations such as the Organization for Economic Cooperation and Development (OECD). If screening provides an early indication of hazard, the guidance will refer to other organizations’ approaches for full-scale toxicological assessment or further tiered studies.