The first purpose of data policy should be to serve the objectives of the organization or project sponsoring the collection of the data. With research data, data policy should also serve the broader goals of advancing scientific and scholarly inquiry and society at large. This is especially true with government-funded data, which likely comprise the vast majority of research data. Data policy should address multiple issues, depending on the nature and objectives of the data. These issues include data access requirements, data preservation and stewardship requirements, standards and compliance mechanisms, data security issues, privacy and ethical concerns, and potentially even specific collection protocols and defined data flows. The specifics of different policies can vary dramatically, but all data policies need to address data access and preservation. Research data gain value with use and must therefore be accessible and preserved for future access. This article focuses on data access. While policy might address multiple issues, at a first level it must address where the data stand on what Lyon (2009) calls the continuum of openness. Making data as openly accessible as possible provides the greatest societal benefit, and a central purpose of data policy is to work toward ethically open data access. An open data regime not only maximizes the benefit of the data, it also simplifies most of the other issues around effective research data stewardship and infrastructure development.