The Dayton trolleybus system forms part of the public transportation network serving Dayton, in the state of Ohio, United States. Opened on April 23, 1933, it presently comprises five lines, and is operated by the Greater Dayton Regional Transit Authority, with a fleet of 45 trolleybuses. In 2023, the system had a ridership of 2,163,400, or about 6,400 per weekday as of the fourth quarter of 2023.

A trolleybus is an electric bus that draws power from dual overhead wires using spring-loaded trolley poles. Two wires, and two trolley poles, are required to complete the electrical circuit. This differs from a tram or streetcar, which normally uses the track as the return path, needing only one wire and one pole. They are also distinct from other kinds of electric buses, which usually rely on batteries. Power is most commonly supplied as 600-volt direct current, but there are exceptions.