This fourth book of the series “Psychoanalysis in 20 Sentences” presents the essential theories of Donald Winnicott , whose ideas transformed psychoanalysis by emphasizing the importance of early relationships, play, and the environment. Written by Brazilian psychoanalyst and philosopher William Marcos , this volume translates complex theoretical concepts into accessible reflections for clinical practice and personal study. Key notions such as the true and false self , the transitional object , and the concept of holding are explained through concise phrases and developed into clinical and theoretical insights. Winnicott’s contributions remain vital for understanding human development, therapy, and the role of the environment in shaping psychic life. This book is intended for psychoanalysts, psychologists, students of mental health, and all readers interested in deepening their knowledge of psychoanalysis. Together with the other volumes—dedicated to Freud, Lacan, Klein, Jung, and Ferenczi—it offers a practical and comprehensive guide to the psychoanalytic tradition.