We are honored and privileged to have assumed editorial responsibilities for the 23rd edition of this iconic, 120-year-old textbook of pediatrics, originated as Diseases of Infancy and Childhood by Dr. Luther Emmett Holt in 1896. The book was published through 11 editions into the 1940s by Dr. Holt and subsequently by his son, Dr. Luther Emmett Holt, Jr., and eventually through another 7 editions by Dr. Abraham Rudolph, who turned Rudolph’s Pediatrics into one of the world’s most widely recognized and read medical textbooks. This 23rd edition represents the first complete transition of editorial responsibilities in more than 40 years. It comes as pediatric practice advances at a dizzying pace. Each new month brings reports in the medical literature of new diagnostic tools and therapeutic strategies. Revolutionary advances in human genomics are illuminating the etiologies and pathogenesis of many of the most vexing medical conditions pediatricians have faced over the course of decades and generations. Fields as diverse as oncology, immunology, and neurology are being transformed by these advances. At the same time, pediatricians are being asked to do more with less, to be more efficient, to provide better patient access, and to become better stewards of the limited resources entrusted to us. We treat children, and families, not diseases, and our patients depend on us to be as straightforward and pragmatic as possible. Change is inherently challenging, but big challenges invariably represent big opportunities. There has never been a better time to be a pediatrician or a more hopeful time to be the parent of a seriously ill child. The years ahead will bring better treatments and more cures for a multitude of medical conditions afflicting children. Our fondest hope is that in the pages of this textbook the reader will find not only relevant facts and information but also the inspiration to do more for the children and families we serve.