Neurodegenerative diseases are major world wide causes of morbidity and mortality. They form a heterogeneous group of diseases, ranging from rare monogenic inherited errors of metabolism to common multi-factorial dementias. Major research efforts focus on the development of disease modifying drugs for neurodegenerative diseases. As a result, there follows a need for reliable tools for diagnosis, prognosis and monitoring of therapy. Processes in the brain can be monitored by analysis of cerebrospinal fluid (CSF). Several CSF biomarkers of pathological processes in the brain are now available. Such biomarkers may be used for both research and in the clinical setting. However, several difficult problems remain to be solved. More intensive collaboration between academia, industry and government is likely needed to develop treatments and biomarkers for neurodegenerative diseases. This article reviews the definitions, usage and current limitations of CSF biomarkers in this field.