The Allen Spinal Cord Atlas is an interactive database of gene expression mapped across all anatomic segments of the mouse spinal cord at postnatal days 4 and 56. The indexed set of images for the entire genome is based on RNA in situ hybridization data, and is searchable and sortable by gene, age, expression, and in the case of the adult, by the cervical, thoracic, lumbar, sacral, and coccygeal segments. Over 80 structures in the cords can be identified with the associated high-resolution Allen Spinal Cord Reference Atlas. This resource represents an unprecedented platform for exploring the spinal cord at the cellular and molecular levels.