The spinal cord constitutes a key structure of the central nervous system. It is involved in the transmission of signals between the brain and the rest of the body through numerous ascending and descending pathways. It also contains relatively simple reflex arcs as well as more complex neuronal circuits that can control central pattern generated-motor behaviors. This section of the book essentially provides a summary description of the functional organization, diseases, and dysfunctions of the spinal cord. It is intended to be a comprehensive review of background knowledge that may be helpful for understanding the chapters that compose the present book on animal models of spinal cord injury.