Starting 1st March 2019 the new Trenitalia Ciampino Airlink combined train and bus service is available which connects the centre of Rome and Ciampino Airport. Located a few metres from the entrance of the airport, the bus connection, which leaves every 20 minutes from the square opposite the airport, takes passengers to the Ciampino Station will making intermediate stop, to the continue the trip towards Termini.

For more information see the Trenitalia  website