Will this requirement apply to travel between the US and Puerto Rico?

The Western Hemisphere Travel Initiative will not affect travel between the United States and its territories.  U.S. citizens traveling between the United States and Puerto Rico will continue to be able to use established forms of identification to board flights and for entry. 

If traveling outside the United States or a U.S. territory, a passport or other secure document will be required.  For example, a person may travel to and from Puerto Rico without a passport or other secure document, but under proposed regulations, a passport or other secure document would be required to re-enter Puerto Rico from the British Virgin Islands, St. Maarten, Dominican Republic or another country as of January 23, 2007.