This book contains anatomical and technical information on aspects of endoscopy of the lumbar subarachnoid space, which was named thecaloscopy. For a surgeon it is important to equip all the knowledge and technological advantages for making diagnosis and treatment of patients. Minimally invasive spinal surgery has been well developed in the last few decades. This book suggests the use of flexible endoscopes to approach the content of the thecal sac in order to scrutinize and cure pathological conditions that originate from this anatomical region and cannot be diagnosed by other means.