Biomarkers support clinical practice in almost every area of medicine and are increasingly used in the assessment of brain diseases. Their role in the diagnosis of dementia is covered in this chapter. Structural neuroimaging should be considered in all patients with suspected dementia. Functional imaging offers additional insights into the biological activity of the brain, providing estimates of regional cerebral blood flow, glucose metabolism, dopamine neurotransmission, and amyloid burden. Certain dementias, notably Alzheimer’s disease, also have a characteristic profile of cerebrospinal fluid biomarkers. The diagnostic roles of these different biomarkers are explored to help guide their application in clinical practice.