The cerebrospinal fluid (CSF) is a dynamic, metabolically active fluid that occupies the subarachnoid space and the ventricular system around the brain, and has many important functions. CSF is a promising body fluid for the search of biomarkers associated with neurological disease, because the CSF has more physical contact with brain than any other fluids, biochemical changes related to many pathology may be reflected in the CSF. Although CSF is obtained by lumbar puncture, invasive and potentially painful for the patient, it is probably the most informative fluid in biomarkers discovery for neurological disease prognosis. This book discusses CSF biomarkers; novel developed biomarkers in neurological diseases; CSF biochemical markers of cerebral metabolism in dogs; and guidance for the selection and interpretation of laboratory tests.