Mild cognitive impairment (MCI) is a syndrome that spans the area between normal ageing and dementia. It is classified into amnestic and non-amnestic types, both with two subtypes: single domain and multiple domains. Prevalence of MCI depends on criteria and population and can vary from 0.1 to 42% persons of older age. In contrast to dementia, cognitive deterioration is less severe and activities of daily living are preserved. Most impaired higher cognitive functions in MCI are memory, executive functions, language, visuospatial functions, attention etc. Also there are depression, apathy or psychomotor agitation, and signs of psychosis. Aetiology of MCI is multiple, mostly neurodegenerative, vascular, psychiatric, internistic, neurological, traumatic and iatrogenic. Persons with amnestic MCI are at a higher risk of converting to Alzheimer's disease, while those with a single non-memory domain are at risk of developing frontotemporal dementia. Some MCI patients also progress to other dementia types, vascular among others. In contrast, some patients have a stationary course, some improve, while others even normalize. Every suspicion of MCI warrants a detailed clinical exploration to discover underlying aetiology, laboratory analyses, neuroimaging methods and some cases require a detailed neuropsychological assessment. At the present time there is no efficacious therapy for cognitive decline in MCI or the one that could postpone conversion to dementia. The treatment of curable causes, application of preventive measures and risk factor control are reasonable measures in the absence of specific therapy.