Portstewart (Port Stíobhaird in Irish) is a town in County Derry, Northern Ireland. It is a seaside resort, often seen as a grander version of neighbouring Portrush. It is known for its sandy beach, popular with surfers.

Portstewart has a convent with attached Convent School sitting on the edge of a cliff which dominates the western end of the promenade. The eastern end of the promenade has a small harbour which has recently undergone refurbishment. The town is also home to three golf courses (under one club - Portstewart Golf Club), made lively by the forceful Atlantic Ocean wind, which continually pushes over the whole town. Previously an infamous student town - the students from the University of Ulster in nearby Coleraine - it has increasingly become an upmarket holiday town with new developments of apartment buildings along the seafront. The town is also home to Morelli's Ice-Cream and Anchor Pub.

Portstewart Strand, a clean two mile long beach has been the most popular attraction of Portstewart for holiday-makers for generations. Now owned by the National Trust, it is one of the most popular Trust properties in the entire UK.

With its northwest-facing aspect the town enjoys some of the most beautiful sunsets in the world. The songwriter Jimmy Kennedy was inspired by one of these when he wrote 'Red Sails in the Sunset'

The town now has an annual Red Sails Festival each July, which in 2004, as with most years, culminated with a dramatic firework display out over the bay with the gathering summer dusk as a backdrop. Over 70,000 people crammed the seafront to watch.

The main street, the Promenade, along the seafront is a very popular place for a stroll and is renowned as one of those few places in the world where, no matter where you came from, you are bound to meet someone you know.

See also: List of towns in Northern Ireland