Vitamin A is a lipid-soluble micronutrient which has resources from animals and plants. This vitamin has many biological activities such as antioxidant, antiaging, and anticancer, as well as embryological development, immune function, vision, skin health, cell differentiation, and proliferation. Vitamin A deficiency continues to be a public health issue in developing countries, especially affecting children and pregnant women. For this reason, vitamin A deficiency has been investigated in different groups such as children and adults, especially during pregnancy and lactation. This section aims to provide an exhaustive summary of vitamin A and its sources and physiological functions in the body and to examine the causes of its deficiency in different groups in the world and in Turkey and its effects on body systems.