Marine Protected Areas (MPAs), according to Executive Order 13158 (May 200), are defined as "an area of the marine environment that has been reserved by federal, state, territorial, tribal or local laws or regulations to provide lasting protection to part or all of the natural and cultural resources therein".  In the U.S., MPAs span a range of habitats including the open ocean, coastal areas, inter-tidal zones, estuaries, and the Great Lakes.  They also vary widely in purpose, legal authorities, agencies, management approaches, level of protection, and restrictions on human uses.

Over the past century, MPAs have been created by a mix of federal, state, and local legislation, voter initiatives, and regulations, each established for its own specific purpose. As a result, the nation’s collection of MPAs (reserves, refuges, preserves, sanctuaries, areas of special biological significance, and others) was fragmented, complex, confusing, and potentially missing opportunities for broader regional conservation through coordinated planning and management. In 2000, the Department of Commerce received a directive to work with federal agencies, states, territories and stakeholders to establish a national systems of MPAs to integrate and enhance the nation's MPAs to improve conservation of the nation’s marine ecosystems, cultural resources, and fisheries by bringing these diverse sites and programs together to work on common conservation objectives.

Central to the effort to develop a national system of MPAs is the development of an inventory of U.S. marine protected areas.  The Marine Protected Areas Inventory (MPA Inventory) is a comprehensive geospatial database designed to catalog and classify marine protected areas within US waters.  In March 2010, the first MPA Inventory was published, including information on over 1,600 sites. 

The MPA Inventory was expanded to include improvement in the capabilities of the Inventory database and to reflect the best available information on MPA resources and management.  In March 2012, a updated version of the MPA Inventory was published with the additional of 100 sites. The Inventory continues to expand, incorporating data on physical, cultural and ecological resources, scientific monitoring activities, major management activities, and legal authority data at the site level.  In order to create a repeatable and robust protocol for data collection and storage that can be replicated on a regional or national scale, this effort is being undertaken in phases. The Inventory data are current through March 2012 and are provided online in both tabular and GIS form, as well as through an interactive web-based data viewer.

The MPA Inventory was developed with extensive input from state and federal MPA programs and drawn from other publically available data. The MPA Center is continually updating and verifying the Inventory data, so and welcomes any new site information, existing site clarifications or updated spatial boundary data. The Inventory data should not be used for regulatory purposes; please consult the Federal Register for the official record.