Atopic dermatitis is a prevalent inflammatory skin condition characterized by itch and dry skin, which affects 15-20% of children and 3-5% of adults. This article reviews epidemiological, clinical and experimental data to provide an overview of the most important disease mechanisms in atopic dermatitis. Genetic predisposition, environmental insults, atopic triggers, complex host immune response and skin barrier changes, and altered skin microbiota are discussed. Whilst our understanding of atopic dermatitis has improved dramatically in recent years, many basic aspects are still not understood. Further research is needed to fully understand this complex skin disease.