The diagnosis of primary progressive aphasia (PPA) is made in any patient in whom a language impairment (aphasia), caused by a neurodegenerative disease (progressive), constitutes the most salient aspect of the clinical picture (primary). The language impairment can be fluent or nonfluent and may or may not interfere with word comprehension. Memory for recent events is relatively preserved although memory scores obtained in verbally mediated tests may be abnormal. Lesser changes in behavior and object recognition may be present but are not the leading factors that bring the patient to medical attention. This selective clinical pattern is most conspicuous in the initial stages of the disease. Progressive nonfluent aphasia and some types of semantic dementia can be considered subtypes of PPA. Initially brought to the attention of contemporary literature 25 years ago, PPA has recently witnessed substantial progress related to its neurolinguistic features, neuroanatomy, imaging, neuropathology, genetics, and risk factors.