What is the difference between tower, approach and en-route controllers?

Tower, approach and en-route controllers work different parts of the same air traffic system. They coordinate with each other so aircraft move safely from the airport to cruise and back again.

Tower controllers often work visually with aircraft and vehicles at the airport. Approach controllers build arrival streams, manage departing traffic and coordinate with towers and area sectors. En-route controllers handle aircraft over larger sectors, usually at higher altitude.

Training point: a controller qualified in one environment is not automatically qualified for another. Ratings, endorsements and local procedures matter. The ATC training guide explains how this fits into the qualification path.