Biomarkers may be used in the dementias to distinguish different aspects of the underlying pathology, detect presymptomatic pathological changes, predict decline or conversion between clinical disease states, and/or monitor disease progression and response to treatment. In this review, the authors discuss the currently available biomarkers, with a particular focus on the three most common neurodegenerative dementias: Alzheimer’s disease (AD), frontotemporal dementia (FTD), and dementia with Lewy bodies (DLB).