The father of American Existential Psychotherapy is generally considered to be Rollo May. Author of such works as Love and Will, The Cry for Myth, and Freedom and Destiny, May was heavily influenced by the writings of the philosopher/theologian Paul Tillich. In developing an existential approach to therapy, May was also influenced by many of the existential philosophers such as Kierkegaard, Nietzsche, and Heidegger.
Existential psychotherapy is a powerful approach to therapy which takes seriously the human condition. It is an optimistic approach in that it embraces human potential, while remaining a realistic approach through its recognition of human limitation. Falling in the tradition of the depth psychotherapies, existential therapy has much in common with psychodynamic, humanistic, experiential, and relational approaches to psychotherapy.
Yalom, who was influenced heavily by May, is one of the great organizers of existential theory. In his book, Existential Psychotherapy, Yalom (1980) organized the breadth of existential theory into four major themes: 1) Death, 2) Freedom (& Responsibility), 3) Isolation, and 4) Meaninglessness. According to Yalom, these four existential realities are the root of most psychological problems and have no ultimate answers. While other existentialists may be more optimistic about the ability of people to find answers to these questions, it is generally agreed that these four issues are central to the human experience.
Another gift of Yalom is his writing. Both May and Yalom were very talented at being able to take abstract, difficult theory and write about it in a language which is much more understandable than many of the other existential writers. While many people are easily intimidated by existential theory, May and Yalom were able to demonstrate that it is accessible and applicable without needing to wade through the often obtuse writings of many existential scholars and practitioners.
In addition to writing one of the most significant texts on existential theory, Yalom added two fictional novels, When Nietzsche Wept and Lying on the Couch. These works are both exceptional fiction and also insightful psychological writing which illuminates existential and psychoanalytic theories. Perhaps Yalom's greatest contributions were his three book which offer case examples of existential therapy. These were written in a way to be beneficial both to therapists and clients and accomplish both very well. His first book of this nature, Every Day Gets a Little Closer: A Twice Told Therapy, was written with a former client, Ginny Elkin. The book contains the journal of Yalom and Elkin during from the therapy process allowing the reader to get a glimpse of both of their interpretations of the therapy process. The next two, Love's Executioner and Mama and the Meaning of Life, were written by Yalom and based primarily off people he worked with during his career, although a couple of partially fictionalized tales are also included.
If you find yourself interested or intrigues by existential therapy either as a consumer (i.e., therapeut or client) or as a therapist, I'd highly recommend Love's Executioner as a place to start. For a general overview of existential theory, please click here.