The first trolleybus was introduced in Germany in 1882. Ernst Werner von Siemens demonstrated his electrically powered Elektromote on 29 April 1882 in Halensee, then a suburb of Berlin.
The Elektromote ran beneath an overhead electrical line and collected power through a small wheeled contact device. It was an experimental vehicle rather than a lasting public transport route, operating on a test track of about 540 metres until 13 June 1882. Even so, its arrangement established the basic trolleybus principle: a rubber-tyred road vehicle supplied continuously by overhead electricity.
The idea did not immediately become a transport standard. Early electrical collection equipment was unreliable, and tramways had the advantage of fixed rails and mature infrastructure. Further experiments followed in France, the United States, and Germany before practical passenger trolleybus systems appeared around the turn of the twentieth century.
A common mix-up is to confuse the 1882 German experiment with the first permanent trolleybus service. The question asks where the first trolleybus was introduced, making Germany the accepted answer.