Ronald David Laing (7 October 1927 – 23 August 1989), usually cited as R. D. Laing, was a Scottish psychiatrist who wrote extensively on mental illness—in particular, psychosis and schizophrenia.

Laing's views on the causes and treatment of psychopathological phenomena were influenced by his study of existential philosophy and ran counter to the chemical and electroshock methods that had become psychiatric orthodoxy. Laing took the expressed feelings of the individual patient or client as valid descriptions of personal experience rather than simply as symptoms of mental illness. Though associated in the public mind with the anti-psychiatry movement, he rejected the label. Laing regarded schizophrenia as the normal psychological adjustment to a dysfunctional social context.

Politically, Laing was regarded as a thinker of the New Left. He was portrayed by David Tennant in the 2017 film Mad to Be Normal.

Laing was born in the Govanhill district of Glasgow on 7 October 1927, the only child of civil engineer David Park MacNair Laing and Amelia Glen Laing (née Kirkwood). Laing described his parents — his mother especially — as being somewhat anti-social, and demanding the maximum achievement from him. Although his biographer son largely discounted Laing's childhood account, an obituary by an acquaintance of Laing asserted that about his parents – "the full truth he told only to a few close friends".

He was educated initially at Sir John Neilson Cuthbertson Public School and after four years transferred to Hutchesons' Grammar School. Described variously as clever, competitive or precocious, he studied classics, particularly philosophy, including through reading books from the local library. Small and slightly built, Laing participated in distance running; he was also a musician, being made an Associate of the Royal College of Music. He studied medicine at the University of Glasgow. During his time in Glasgow, he set up a "Socratic Club", of which the philosopher Bertrand Russell agreed to be president. Laing failed his final exams. In a partial autobiography, Wisdom, Madness and Folly, Laing said he felt remarks he made under the influence of alcohol at a university function had offended the staff and led to him being failed on every subject including some he was sure he had passed. After spending six months working in a psychiatric unit, Laing passed the re-sits in 1951 to qualify as a medical doctor.

Laing spent a couple of years as a psychiatrist in the British Army Psychiatric Unit at Netley, where, as he later recalled, those trying to fake schizophrenia to get a lifelong disability pension were likely to get more than they had bargained for as insulin shock therapy was being used. In 1953, Laing returned to Glasgow, participated in an existentialism-oriented discussion group, and worked at the Glasgow Royal Mental Hospital. The hospital was influenced by David Henderson's school of thought, which may have exerted an unacknowledged influence on Laing; he became the youngest consultant in the country. Laing's colleagues characterised him as "conservative" for his opposition to electroconvulsive therapy and the new drugs that were being introduced.

In 1956, Laing went to train on a grant at the Tavistock Clinic in London, widely known as a centre for the study and practice of psychotherapy (particularly psychoanalysis). At this time, he was associated with John Bowlby, D. W. Winnicott and Charles Rycroft. He remained at the Tavistock Clinic until 1964.

In 1965, Laing and a group of colleagues created the Philadelphia Association and started a psychiatric community project at Kingsley Hall, where patients and therapists lived together. The Norwegian author Axel Jensen contacted Laing at Kingsley Hall after reading his book The Divided Self, which had been given to him by Noel Cobb. Laing treated Jensen, and subsequently, they became close friends. Laing often visited Jensen on board his ship Shanti Devi, which was his home in Stockholm.