The prevalence of atopic dermatitis (AD), the most common inflammatory skin disease in children, has increased over the last decade. Although there is a genetic predisposition to AD, there is strong evidence suggesting a crucial role for environmental factors. The etiology of AD is probably multifactorial and includes interactions between the genetic predisposition and exogenous provocation factors. Many specific exogenous factors have been associated with the disease. These factors include, house dust mites, irritants, dietary allergens, air pollution, etc. In this chapter, we try to review the most important factors that have been implicated in the etiology of AD.