Up until two decades ago, clinical interest in the etiopathogenetic interpretation of lumbo-radicular syndromes was prevalently concentrated on the pathology of the inter­ vertebral disc. This vision gradually changed and grew as a result of the affirmation of the concept of pathological narrowing of the osteoligamentous vertebral canal as a cause of compression of the lumbar nervous structures. Finally, in the last ten years, lumbar stenosis has become more and more a subject of current interest not only as a result of problems related to nosography, diagnosis, and therapy, but also as a result of the increasing frequency with which vertebral canal or nerve root canal stenosis syndromes are recognized and treated. At the same time there was a tendency to include in stenotic pathology other pathological conditions responsible for lumbo-radicular syndromes. This led to dilation of the concept of stenosis, which perhaps no longer responded to reality, and which was not useful from a practical point of view. The need to define stenotic pathology and to correctly locate it within the vast field of lumbar pathology inspired the writing of this volume. This monograph gathers many diagnostic and therapeutic concepts matured at our In­ stitution over the years. Some of these concepts have already been defined in scientific meet­ ings or in publications.