Panama Canal Zone, a strip of land across the Isthmus of Panama that the United States controlled from 1903 to 1979. The zone extended about five miles (8 km) on each side of the Panama Canal and covered 553 square miles (1,432 km2), including 191 square miles (495 km2) of water. It had been granted to the United States by a treaty with the Republic of Panama for the purpose of building, operating, and maintaining the canal.

The Hay-Bunau-Varilla Treaty, signed in 1903 and ratified in 1904, recognized Panama's independence and established the Canal Zone. The zone was administered by the Canal Zone Government, and the canal was operated by the Panama Canal Company. Both were United States government agencies.

Long-standing resentment over the existence of the Canal Zone led to rioting by Panamanians in 1964. After years of negotiations, two new treaties were drawn up—the Panama Canal Treaty, which called for the United States to turn over the Canal Zone and, in 1999, the canal to Panama; and the Neutrality Treaty, which provided for the canal's perpetual neutrality. Both were ratified by the U.S. Senate in 1978. On October 1, 1979, the Canal Zone ceased to exist, becoming part of Panama.