Rollo Reece May (April 21, 1909 – October 22, 1994) was an American existential psychologist and author of the influential book Love and Will (1969). He is often associated with humanistic psychology and existentialist philosophy, and alongside Viktor Frankl, was a major proponent of existential psychotherapy. The philosopher and theologian Paul Tillich was a close friend who had a significant influence on his work.

May's other works include The Meaning of Anxiety (1950, revised 1977) and The Courage to Create (1975), named after Tillich's The Courage to Be.

Reese May, otherwise known as 'Rollo' May, was born in Ada, Ohio, on April 21, 1909 to Matie Boughton and Earl Tittle May, a Men's Christian Associations Field Secretary, as the first son and the second eldest of six.

His namesake 'Rollo', or, as his Mother called him, 'Little Rollo', was the title character from a series of children's' books. written by Jacob Abbott in the 19th century. Rollo was reported to have an intense dislike for this nickname; however, he made his peace with the moniker after learning about Rollo the Conqueror, a tenth century Norman.

Some may describe Rollo's childhood as difficult due to the divorce of his parents and to his oldest sister's struggle with mental health that resulted in frequent hospitalizations. His mother often left the children alone, and with his sister suffering from schizophrenia, he bore much of the burden. At Michigan State University he majored in English, but was expelled due to his involvement in a radical student magazine. After that, he attended Oberlin College and received a bachelor's degree in English. He spent three years teaching in Greece at Anatolia College. During this time, he studied with doctor and psychotherapist Alfred Adler, with whom his later work shares theoretical similarities. He was ordained as a minister shortly after coming back to the United States, but left the ministry after several years to pursue a degree in psychology. He was diagnosed with tuberculosis in 1942 and spent 18 months in a sanatorium. He later attended Union Theological Seminary for a BD during 1938, and Teachers College, Columbia University for a PhD in clinical psychology in 1949. May was a founder and faculty member of Saybrook Graduate School and Research Center in San Francisco.

He spent the final years of his life in Tiburon on San Francisco Bay. May died of congestive heart failure at the age of 85, attended by his wife, Georgia, and friends.

When beginning his first books, May's topics focused on more practical uses regarding patients and mental health. His first book, The Art of Counseling (1939) talks about his experience of counseling. Some of the topics he looks at are empathy, religion, personality problems and mental health. May also gives his perspective on these and also discusses how to handle those particular types of issues should a counselor encounter them (May 1965). He followed with a more theoretical book, The Springs of Creative Living: A Study of Human Nature and God (1940) presenting a personality theory influenced by critiquing the work of others, including Freud and Adler. He claims that personality is deeper than they presented. This is also where May introduces his own meaning for different terms such as libido from Freudian Psychology (May, 1940).

His writings were interrupted in the 1940s due to being diagnosed with tuberculosis and having to work on his PhD.