Ume Eder Bat (A beautiful child) (popular song from Basque folklore) The aim of this monograph is to introduce the postnatal development of morphological features that are relevant to readers interested in the neurobiology and pathology of the hippocampal formation in terms of the complex phenomena that underlie the progressive anatomical and functional maturation of this brain region. This review focuses on the morphological aspects, while more detailed basic phenomena associated with neuronal maturation-which are undoubtedly also of great interest-are only marginally referred to, although a selection of behavioral and clinical aspects will also be briefly addressed in an attempt to illustrate real situations in different clinical specialties. The creation of this monograph is justified by the increasing importance and growing awareness shown in recent years of neurodevelopmental disorders in children. This awareness is leading to increasing refinement in clinical exami- tions of patients that may suffer from different neurodevelopment-related diseases, such as autism, epilepsy, memory disorders, etc. To the best of our knowledge, this work is the first comprehensive description of the postnatal changes in the hip- campal formation in its different constituent fields. Given the growing sensitivity and accuracy of neuroradiological examinations, particularly MRI, we also sought to offer a glimpse at the MRI aspects related to the development of the hippocampal formation in the human infant.