There are two "official" definitions of metropolitan area used today in the United States, metropolitan statistical areas, and combined statistical areas, the former restrictive, the latter more extensive. The following is a list (by population) of all metropolitan statistical areas as defined by the United States Census Bureau.
Population estimates are current as of July 1, 2006. Metropolitan statistical area names are current as of December 1, 2005.
Several of these areas extend into Canada or Mexico but are not recognized by the US Census Bureau; US Census population figures do not include sections of cross-border metropolitan areas outside of the United States.

The Census Bureau does not include Puerto Rico in its overall rankings of areas.