Bridget Louise Riley CH CBE (born 24 April 1931) is an English painter known for her op art paintings. She lives and works in London, Cornwall and the Vaucluse in France.

Riley was born on 24 April 1931 in Norwood, London. Her father, John Fisher Riley, originally from Yorkshire, had been an Army officer. He was a printer by trade and owned his own business. In 1938, he relocated the printing business, together with his family, to Lincolnshire.

At the beginning of World War II, her father, a member of the Territorial Army, was mobilised, and Riley, together with her mother and sister Sally, moved to a cottage in Cornwall. They shared the cottage with an aunt who had studied at Goldsmiths' College, London and Riley attended talks given by a range of retired teachers and non-professionals. She attended Cheltenham Ladies' College (1946–1948) and then studied art at Goldsmiths' College (1949–52), and later at the Royal College of Art (1952–55).

Between 1956 and 1959, she nursed her father, who had been involved in a serious car crash. She suffered a breakdown due to the deterioration of her father's health. After this she worked in a glassware shop. She eventually joined the J. Walter Thompson advertising agency, as an illustrator, where she worked part-time until 1962. The Whitechapel Gallery exhibition of Jackson Pollock in the winter of 1958 had an impact on her.

Her early work was figurative and semi-impressionist. Between 1958 and 1959, her work at the advertising agency showed her adoption of a style of painting based on the pointillist technique.

In 1959, Riley met the painter and art educator Maurice de Sausmarez at a residential summer school that he ran with Harry Thubron and Diane Thubron. He became her friend and mentor, inspiring her to look closer at Futurism and Divisionism and artists such as Klee and Seurat. Riley and de Sausmarez began an intense romantic relationship later that year and spent the summer of 1960 together painting in Italy where they visited the Venice Biennale which was hosting a large exhibition of Futurist art. Riley painted Pink landscape (1960), a pointillist study of the landscape near Radicofani during this holiday. When the relationship ended in autumn of the same year, Riley suffered a personal and artistic crisis, creating paintings that would lead to black and white Op Art works, such as Kiss (1961). She began to develop her signature Op Art style consisting of black and white geometric patterns that explore the dynamism of sight and produce a disorienting effect on the eye and produces movement and colour. Riley and de Sausmarez maintained a professional friendship until his death in 1969. Riley has often cited his role as an early mentor and de Sausmarez's monograph on Riley and her work was published after his death in 1970.

Early in her career, Riley worked as an art teacher for children from 1957 to 1958 at the Convent of the Sacred Heart, Harrow (now known as Sacred Heart Language College). At the Convent of the Sacred Heart, she began a basic design course. Later she worked at the Loughborough School of Art (1959), Hornsey College of Art, and Croydon College of Art (1962–64).

In 1961, she and her partner Peter Sedgley visited the Vaucluse plateau in the South of France, and acquired a derelict farm which they eventually transformed into a studio. Back in London, in the spring of 1962, Victor Musgrave of Gallery One held her first solo exhibition.