Claude Michel Steiner (6 January 1935 – 9 January 2017) was a French-born American psychotherapist and writer who wrote extensively about transactional analysis (TA). His writings focused especially on life scripts, alcoholism, emotional literacy, and interpersonal power plays.

In the 1970s and 1980s, Steiner was a founder and practitioner of Radical Psychiatry, a new approach to psychotherapy based in a social theory (of alienation) rather than a medical one (of individual pathology). Influenced by progressive movements of the time, work in this modality continues into the present and is gaining recent recognition worldwide. He was also considered the originator of the theory called Stroke Economy, in collaboration with Hogie Wyckoff.

Steiner was born in Paris, France. His parents were Austrian, his mother Ashkenazi Jewish and his father white. The family left France in 1939 ahead of the impending Nazi invasion. Eventually the family settled in Mexico. In 1952, Steiner went to the United States to study engineering. In 1957 he met and became a follower of Eric Berne, a psychiatrist and founder of the transactional analysis school of psychotherapy. In 1965 he obtained a PhD in clinical psychology at the University of Michigan, Ann Arbor. He was a founding member and teaching member of the International Transactional Analysis Association.

The Radical Psychiatry movement was borne out of the greater anti-psychiatry movement of the 1960's and continues to this day. The movement's key critiques and philosophies have their roots in the work of thought leaders, R.D. Laing, Thomas Szasz, Frantz Fanon, Herbert Marcuse, Erich Fromm, Wilhelm Reich, and notably Eric Berne, the originator of transactional analysis, who was one of Steiner's primary mentors. In 1969, Steiner joined the Berkeley Free Clinic to start a psychological counseling center to practice an early form of Radical Psychiatry, and in part to address the emotional needs of the influx of mostly white young people drawn to the Bay Area by stories of "flower-child" utopia. Shortly after, he was joined by Hogie Wyckoff and Joy Marcus, later to become leading feminist thinkers, who contributed key theoretical foundations to a theory of Radical Psychiatry, which were later published in an early "Manifesto" written by Steiner & Wyckoff to be distributed at the American Psychology Association conference San Francisco in September 1970 as a part of a coalition of women, homosexuals, mental patients, and others who felt oppressed by psychiatric practice and organized to disrupt the meeting.

While Steiner's training with Berne gave him prowess as a therapist and an outsider lens on the practice of psychiatry and psychology, along with a platform and resources to explore ideas, others contributed many of the core concepts of Radical Psychiatry. Steiner encouraged development of the theory and was dutiful in sharing credit. In particular, Hogie Wyckoff's grounding in feminism and Marxism contributed significant key ideas such as the "Pig Parent", alienation as the root of mental disorders, and the stroke economy while Joy Marcus' community organizing experience highlighted isolation as a key component of alienation and the need for political action, not just awareness, to address alienation. Other key contributors to Radical Psychiatry theory were Robert Schwebel (who initially developed their theory of cooperation), Becky Jenkins (who developed a robust approach to mediations), Darca Nicholson (who contributed bodywork as a key component of the work) and Beth Roy (who further developed models of power analysis, and significantly furthered their approach to mediations, amongst other contributions). Many of these contributors were also recruited and initially trained by Steiner in Transactional Analysis and group work.

This core group all practiced within the "RAP Center" (also called the Radical Psychiatry Center), along with many others who, together, offered daily drop-in "problem solving" groups free to anyone who needed them in a dedicated building. However, as theoretical controversies developed, dozens of collective groups were reduced down to a handful of people (in particular those mentioned above) which continued meeting for two decades. This group, referred to as the Bay Area Radical Psychiatry Collective (BARP), published a quarterly journal "Issues in Radical Therapy" , an annual 4-day event referred to as the Summer Institute - a teaching institute, eclectic conference, and celebration of a national network, and a collectively drafted manual outlining the practices of Radical Psychiatry (edited by Roy and Steiner). Many of the BARP members also lived together in collective housing during this time.

Separately, in 1970, a Radical Therapy Collective from Minot, North Dakota started an anti-psychiatry publication named "The Radical Therapist." Steiner, along with other members of the BARP, contributed articles in The Radical Therapist, until the publication changed its name in 1972 to the Rough Times, due to an ideological turn in its organizers and readership away from any association with the institution of therapy and towards mental health patient organizing against psychiatric incarceration and other staunch anti-psychiatric activities. Around the mid 1970s, psychiatry in the U.S. became more about prescribing drugs and since there was an existing greater movement from many independent sources towards radicalizing therapy, the BARP started referring to themselves as Radical Therapists.

By 1979, the BARP experienced critique due to the power the group accumulated through their success in publishing and teaching. Their authority began to resemble an institution, the very thing they had set out to deconstruct. The group also reported experiencing internal dynamics of burnout and overblown sense of responsibility, and for these reasons, they disbanded and gave away the Issues in Radical Therapy to a group in Colorado and the Summer Institute to a group in San Francisco, which both shortly thereafter ceased activities. However, the practice of Radical Psychiatry continues across the U.S. as well in Germany and other European countries, where it is combined with Co-counselling practices. While the movement was originally largely white, in part due to the demographics of Berkeley in the 60s and 70s, this is changing in modern practice of Radical Psychiatry.