This toolkit is part of the CESSDA SaW project cost-benefit advocacy programme. The toolkit has been developed for its primary audience of staff in existing or proposed national social science archives in Europe. The major use for the toolkit will be supporting funding and business cases but elements are likely to be relevant in advocacy to other groups or in supporting broader operational tasks. This toolkit is comprised of: - A User Guide; - Three Factsheets (Benefits, Costs, and Return on Investment); - Four Case Studies from Social Science Data Archives (ADP in Slovenia, FSD in Finland, LiDA in Lithuania, and UKDS in the UK); - Two Worksheets (the Archive Development Canvas, and the Benefits Summary for a Data Archive).