Frontotemporal dementia (FTD) is an important cause of non-Alzheimer's dementia and is the second most common cause of young onset dementia. FTD presents with progressive changes in behavior and personality (behavioral variant FTD) or language deficits (also known as primary progressive aphasia), although both commonly coexist. Patients with progressive aphasia are subclassified according to the pattern of language deficits into those with progressive non-fluent aphasia (PNFA) and semantic dementia (SD). FTD is pathologically heterogeneous, both macroscopically and on a molecular level, with tau positive, TDP-43 positive, and FUS positive intraneuronal inclusions recognized on immunohistochemical analysis. TDP-43 positive inclusions are also a feature of amyotrophic lateral sclerosis pathology, corroborating the observation of overlapping clinical features between the two conditions and reaffirming the FTD-ALS disease spectrum. Most FTD cases are sporadic, but an important minority is inherited in an autosomal dominant fashion, most commonly due to MAPT or progranulin gene mutations. Familial clusters of FTD and amyotrophic lateral sclerosis are also recognized but poorly understood. This paper reviews the clinical phenotypes, assessment and treatment of FTD in light of recent pathological and genetic discoveries.