Since 2011, the National Science Foundation (NSF) has required that all grant proposals include a Data Management Plan describing how the proposal will conform to NSF policies on the dissemination and sharing of research results. Proposals that do not include a Data Management Plan cannot be submitted through the Grants.gov proposal submission interface.
As of summer 2015, NSF is in the process of updating its requirements for Public Access to results of NSF-funded Research. In addition to the current requirements for data management plans, the updated NSF policy appears likely to require that grantees deposit data in “a public access compliant repository designated by NSF.” This NSF requirement will apply to new awards resulting from proposals submitted, or due, on or after the effective date of the Proposal & Award Policies & Procedures Guide (PAPPG) that will be issued in January 2016.
From the NSF's current Dissemination and Sharing of Research Results:
Investigators are expected to share with other researchers, at no more than incremental cost and within a reasonable time, the primary data, samples, physical collections and other supporting materials created or gathered in the course of work under NSF grants. Grantees are expected to encourage and facilitate such sharing. See Award & Administration Guide (AAG) Chapter VI.D.4.
Proposals submitted or due on or after January 18, 2011, must include a supplementary document of no more than two pages labeled “Data Management Plan”. This supplementary document should describe how the proposal will conform to NSF policy on the dissemination and sharing of research results. See Grant Proposal Guide (GPG) Chapter II.C.2.j for full policy implementation.
Key elements of an NSF Data Management Plan include:
Other relevant information from NSF:
Unidata has a sample Data Management Plan for an NSF proposal here.