Bartolomeo Eustachio (1520-1574), a major anatomist and physician of the Italian Renaissance, made very significant contributions toward our knowledge of the anatomy and physiology of the dentition, including the first descriptions of the structure of the dental pulp and of the periodontal membrane. His treatise on the teeth, "Libellus de Dentibus", published in 1563, has just been translated into English, and the remarkable descriptions of the dental pulp, the periodontal membrane, the development of both sets of teeth from dental follicles, the trigeminal nerve, and other oral structures have not been fully appreciated. We offer extensive translated material from his treatise to establish the unique insight that Eustachio had into the structure and function of the human dentition, based upon extensive dissections of both human and animal material. Eustachio also had very modern ideas concerning the treatment of periodontitis, including the curettage of granulation tissue to promote reattachment of the gingival tissue.