This article aims to review the expanding role of group psychotherapy in the treatment of individuals with medical illnesses, an area that has expanded dramatically during the past 30 years. The fundamental principles of adaptation of group therapies for specialized clinical populations are articulated. Clarity of goals and thoughtful alignment with patient interests and needs are at the heart of building a strong therapeutic alliance and potentiate the effectiveness of group therapy. This article also discusses the conceptual underpinnings of group therapies and the ways in which group therapeutic factors gain expression with these clinical populations. This article also focuses on breast cancer, in light of its clinical prominence and the development of group therapies for individuals with the disease. These therapies address clinical concerns for women along the continuum of the disease, including familial and genetic predisposition, primary breast cancer, adaptation to illness and its treatment, metastatic disease, and dealing with mortal illness.