We describe the most complete and best−preserved materials assigned to Simocyon from Spain. Specimens come from the late Miocene (Vallesian) locality of Batallones−1, Province of Madrid and are assigned to Simocyon batalleri. Cranial, mandibular and dental anatomy of S. batalleri from Batallones−1 is described and compared with those of known species of Simocyon. We review the systematic status and the definition of the species of Simocyon and we analyse the morphological variation within Simocyon. Three species are recognized as valid. S. batalleri is known from several Vallesian localities (mainly MN 10) of Spain. S. diaphorus, from the early Vallesian of Germany (Mammal Zone MN 9), is the geologically oldest European species. The type species S. primigenius is Turolian in age and known from several localities of Europe, North America, and China. The species includes the junior synonyms S. zdanskyi and S. marshi. The status of Simocyon hungaricus is not resolved. Simocyon simpsoni is excluded here from Simocyon and reassigned to its original generic name Protursus. On the basis of the material described here, we propose a differential diagnosis for Simocyon batalleri. This species is morphologically intermediate between the more primitive S. diaphorus, which has a less reduced p3; and the more derived S. primigenius, characterized by a modified mandible (e.g., more vertical and more expanded coronoid process, longer angular process). The evolution of the genus Simocyon is characterized by a trend toward a more crushing adaptation involving at least a modification of the posterior part of the mandible. A reconstruction of the skull and life appearance of Simocyon is proposed.