The Middle Pleistocene time period is characterized by considerable debate among researchers, with taxonomic and phylogenetic questions centering around evolutionary relationships between European and African fossils and the origins of both the Neandertals and modern humans. Nevertheless, these debates have been hampered by a widely-scattered and poorly-dated hominin fossil record. The current symposium focuses on the evidence from the large fossil assemblage from the Sima de los Huesos in the Sierra de Atapuerca in northern Spain and addresses a number of the most relevant issues regarding fossil hominin morphology, taxonomy and phylogenetic relationships during this time period. This site offers the unique opportunity to study the skeletal remains of a single, well-dated and contemporaneous Pleistocene population and, importantly, provides critical evidence from both the skull and the postcranial skeleton. An argument is made that this collection is critical for understanding and clarifying the course of human evolution in Europe during this time period.