Pio del Rio-Hortega, one of the pioneering neuroscientists and discoverer of microglia, has been recognized as one of the most important Spanish neurohistogists of the past century. His landmark research on oligodendroglia, originally published in Spanish in 1928, has been translated into English for the first time by Dr. Jose R. Iglesias-Rozas and Prof. Manuel Garrosa. The book establishes definitively the concept of oligodendroglia and describes in great detail its structure, varieties, function, origin and pathology, providing a thorough review. The entire 1928 writing is presented, including the 79 excellent drawings and photographs from the original publication. To complement the original book and provide historical context, the translators have also included an introduction to the research and a biography of Pio del Rio-Hortega. This book constitutes a milestone in the history of neuroscience, biology and medicine, and it will be valuable reading for researchers and practitioners in these fields.