Lumbar puncture is the original neurological procedure. The technique is learned by the student first through observation then performance under supervision by a physician who has mastered the technique. It is one of the more difficult procedures in medicine because success is not only dependent on the skill of the physician but also the size, anatomy, and comfort of the patient. The technique, complications, contraindications, and treatment of the complications are reviewed. A discussion of the composition of normal cerebrospinal fluid (CSF) is included, as well as tables for diagnostic CSF studies for infectious, inflammatory, and neoplastic central nervous system disorders.