Cerebrospinal fluid (CSF) collection and laboratory analysis are recommended as part of the investigation of central nervous system (CNS) disease. A definitive daignosis on the basis of CSF laboratory evaluation alone is rare, but the laboratory evaluation of CSF may provide documentation of normal or abnormal findings and help make distinctions among various differential diagnoses. This chapter covers CSF collection, laboratory analysis of CSF, normal and abnormal CSF and CSF findings in selected clinical conditions. Case examples are included.