Irvin D. Yalom and Molyn Leszcz's The Theory and Practice of Group Psychotherapy is the definitive text on conducting therapeutic groups, now in its sixth edition. Yalom, a psychiatrist and novelist whose work has shaped the field for over fifty years, articulates the eleven therapeutic factors that make groups effective, including universality (realizing one is not alone), altruism (helping others), and interpersonal learning. The book integrates theoretical foundations with practical guidance, addressing how to compose groups, manage difficult members, handle critical incidents, and work through termination. This edition, coauthored with Leszcz, incorporates a decade of new research on trauma, mindfulness-based approaches, and online groups. Yalom's distinctive voice combines clinical wisdom with philosophical depth; he treats group therapy not merely as technique but as an encounter with fundamental human concerns about meaning, isolation, and mortality. The book includes numerous clinical vignettes that bring concepts to life. While primarily intended for mental health professionals, the writing is clear enough to benefit anyone interested in group dynamics and interpersonal relationships. The Theory and Practice of Group Psychotherapy has trained generations of therapists and remains the essential reference in its field.