Dayton is a city in southwestern Ohio, United States with a population of 166,179 (2000). It is the county seat and largest city of Montgomery County. The Greater Dayton area or Dayton metropolitan area encompasses a number of contiguous communities outside Dayton city proper, including Vandalia, Trotwood, Kettering, Centerville and Beavercreek, with a population of 848,153 (2000). Dayton is situated within the Miami Valley region of Ohio, just north of the Cincinnati metropolitan area.

Dayton plays host to significant industrial, aerospace, and research activity and is known for the many technical innovations and inventions developed there. The city was the home of the Wright Brothers, poet Paul Laurence Dunbar, and entrepreneur John H. Patterson. Dayton is nicknamed the Gem City, and is also sometimes referred to as the "Birthplace of Aviation."

Dayton Sister Cities International supports efforts for business and cultural development in Augsburg, Germany; Belgrade, Serbia; Oiso, Japan; Monrovia, Liberia; Holon, Israel and Sarajevo, Bosnia and Herzegovina.