Trainer is a borough in Delaware County, Pennsylvania, United States.

The borough was named after David Trainer, a wealthy textile manufacturer.

It is bordered to the southwest by the borough of Marcus Hook, to the west by the community of Linwood in Lower Chichester Township, to the north by Upper Chichester Township, to the east by the city of Chester, and to the south across the Delaware River by Gloucester County, New Jersey.

Stoney Creek passes through the town, emptying into the Delaware River.

The shore of the Delaware River is heavily industrialized and is an extension of the Port of Chester.

The Stoney Creek Secondary has a rail yard north of its namesake.

Trainer previously was served by Resurrection of Our Lord School in Chester.

27.1% of all households were made up of individuals, and 12.4% had someone living alone who was 65 years of age or older.