If you plan to fly across the border, you better have your passport in hand. Starting October 1, U.S. citizens traveling by air outside the United States will have to carry a passport.
The U.S. Departments of State and Homeland Security will no longer accept an official proof of passport application. This requirement comes from the Western Hemisphere Travel Initiative, which Congress mandated in 2004. The passport rule went into effect Jan. 23 this year but was eased from June 8 to Sept. 30 because the influx of U.S. citizens applying for passports caused a backlog.