The Gateway Arch is a 630-foot-tall (192 m) monument in St. Louis, Missouri, United States. Clad in stainless steel and built in the form of a weighted catenary arch, it is the world's tallest arch and Missouri's tallest accessible structure. Some sources consider it the tallest human-made monument in the Western Hemisphere. Built as a monument to the westward expansion of the United States and officially dedicated to "the American people", the Arch, commonly referred to as "The Gateway to the West", is a National Historic Landmark in Gateway Arch National Park and has become an internationally recognized symbol of St. Louis, as well as a popular tourist destination. It is also listed on the National Register of Historic Places.

The Arch was designed by the Finnish-American architect Eero Saarinen in 1947, and construction began on February 12, 1963 and was completed on October 28, 1965, at an overall cost of $13 million (equivalent to $92.6 million in 2018). The monument opened to the public on June 10, 1967. It is located at the 1764 site of the founding of St. Louis on the west bank of the Mississippi River.