Rathgar, originally a village, from 1862 part of the township Rathmines and Rathgar, in 1930 became a suburb of Dublin, Ireland. It lies about 3 kilometres south of the city centre.

Rathgar is situated in south Dublin. It lies beside Rathmines, Terenure, Dartry and Harolds Cross. Other nearby suburbs are Ranelagh, Rathfarnham, Milltown, Kimmage and Crumlin. The Grand Canal lies directly north of Rathgar. The majority of Rathgar lies within the jurisdiction of Dublin City Council, and straddles the postal boundary of Dublin 6.

Rathgar, in the Middle Ages, was a farm belonging to the Convent of St Mary de Hogges, at present-day College Green. At the Dissolution of the Monasteries, Rathgar was granted to the Segrave family: they built Rathgar Castle, ownership of which subsequently passed to John Cusack, who was Lord Mayor of Dublin in 1608. The castle remained in the possession of the Cusack family for over a century, but gradually decayed and was a ruin by the end of the eighteenth century. No trace of it remains today: it is thought to have been located at what is now 44-49 Highfield Road.

The village began to develop in the eighteenth century: Rathgar Avenue is probably the oldest street, while Highfield Road was developed in 1753. Zion Church and Christ Church Rathgar were built in the 1860s, by which time Rathgar was a sizeable community.

Rathgar has a variety of retail outlets. It maintains a village feel and has a delicatessen, 2 butchers, a bike shop and a wine shop within 20 yards of the main cross. There is also Rathgar Pharmacy, Rathgar Hair Studio and a number of fashion and interior boutiques. There is also a small Supervalu supermarket. Local restaurants include Bijou (Modern Irish), Lumanti of Nepal (Nepalese), Howard's Way and Kanum (Asian).

The Dublin Jewish Progressive Congregation (Knesset Orech Chayim) have their Synagogue at 7 Leicester Avenue, Rathgar. Leicester Avenue is a continuation of Kenilworth Square, South. The orthodox Dublin Hebrew Congregation have their synagogue in nearby Terenure