To ensure that the tests used to address the safety of Manufactured Nanomaterials are consistent and defensible; the OECD launched the Sponsorship Programme for the Testing of Manufactured Nanomaterials (Testing Programme) in November 2007. This Testing Programme verifies the testing methods used on Manufactured Nanomaterials by pooling the expertise of OECD member countries, some non-member countries and other stakeholders to fund the safety testing of specific Manufactured Nanomaterials. This dossier on Synthetic Amorphous Silicon dioxide (SAS) provides an overview of the outcomes of the testing as well as background information and including a review of relevant literature. Detailed information on results is presented in the appendices to this report.