For the first time, the complete writings of Donald W. Winnicott are brought together, compiled, edited, and commented on by a team of Winnicottian scholars. Presented chronologically in 12 volumes, the Complete Works of the English psychoanalyst constitute a set of clinical observations, children's consultations, psychoanalytic texts, correspondence, as well as unpublished works on topics that continue to be of interest to contemporary readers (such as mental health in childhood, motherhood, or her concepts of "good enough mother" and "transitional object"). In these Complete Works the reader will be able to find an introduction to each volume by specialists in the work of Winnicott, which in this first volume is by Ken Robinson, preceded by a general introduction to the Complete Works by its editors Lesley Caldwell and Helen Taylor Robinson, who have also done an exhaustive work of notation and comments of great clinical value and that provide context for each of Winnicott's works. For this edition in Spanish, a notation work was also carried out that marks the choice of certain concepts over others, accompanied by a prologue and introduction by the committee in charge of the translation into our language. This first volume, entitled Letters to the family, pediatric writings and the manic defense inaugurates the publication in Spanish of the Complete Works of Donald W. Winnicott. We hope that all Spanish-language readers can enjoy them, as well as all people who are interested in the field of psychoanalysis and childhood.