Neuropsychology contributes greatly to the diagnosis of dementia. Cognitive deficits can be detected several years before the clinical diagnosis of dementia. The neuropsychological profile may indicate the underlying neuropathology. Neuropsychological assessment at an early stage of dementia has two goals: (a) to determine a memory disorder, not always associated with a memory complaint, and (b) to characterize the memory disorder in light of the cognitive neuropsychology and to assess other cognitive (and noncognitive) functions toward integrating the memory disorder in a syndrome. We review the global tools, the memory tests that describe the memory profile and indicate the underlying pathology, the assessment of other cognitive functions, and the neuropsychological patterns of typical Alzheimer's disease, frontotemporal dementia, primary progressive aphasia, semantic dementia, Lewy body dementia, subcortical dementia, and vascular dementia. These patterns must be interpreted in the light of the history, rate of progression, imaging results, and nature of existing behavioral disturbances. Moreover, there may be overlap between two or more pathologies, which complicates the diagnostic process. Follow-up of patients is necessary to improve diagnostic accuracy.