The majority of neurodegenerative diseases are characterized by the deposition of insoluble protein in cells of the neuromuscular system. Advances in molecular neuropathology have allowed a classification system of neurodegenerative diseases based on this protein accumulation. Microtubule-associated tau is one protein that has important functions in healthy neurons, but forms insoluble deposits in diseases now known collectively as tauopathies. Tauopathies encompass more than 20 clinicopathological entities, including Alzheimer's disease, the most common tauopathy, progressive supranuclear palsy, Pick's disease, corticobasal degeneration and post-encephalitic parkinsonism. There are important clinical, pathological, biochemical and genetic similarities in the range of these diseases and they have helped to advance our understanding of the aetiological factors that initiate neurodegeneration and tau accumulation. This review examines the important clinical features of the most prevalent tauopathies and the molecular and pathological features that underpin the classification system.