The incidence of Alzheimer’s disease (AD) increases exponentially with age. Therefore, it becomes a major public health problem since the population is getting older, and the cost of caring increases. Cognitive deficits in AD appear and progress insidiously, but the rate of progression can vary. The average life expectancy has been reported to be between three and eight years. Clinical assessment and neuropsychological testing are necessary initial tools for the diagnosis of AD. Memory impairment, specifically loss of episodic memory (memory of recent events), is an essential feature of AD and is usually its first manifestation. Deficits in other cognitive domains may appear with or after the development of memory impairment. Language function and visuospatial skills tend to be affected relatively early, while deficits in executive function and behavioural symptoms often manifest later in the disease course. Neuropsychiatric and behavioural symptoms are common in middle and late stages of AD. Noncognitive neurologic deficits (pyramidal and extrapyramidal motor signs, myoclonus, and seizures) can occur in late stages of AD, but are uncommon in early and middle stages. Atypical presentations of AD may occur. These include a visual variant (posterior cortical atrophy), primary progressive aphasia (PPA) and behavioural variant AD (bvAD). AD progresses through three stages: an early, preclinical stage with no symptoms; a middle stage or mild cognitive impairment (MCI); and a final stage marked by symptoms of dementia (apparent AD). Diagnostic tests (basic laboratory tests and neuroimaging) are performed initially to exclude other (treatable) causes. Recently discovered biomarkers may help in early and differential diagnosis as well as prognosis of AD.