This lecture provides a general overview of epithelial barriers and innate immunity, highlighting the historical background and the importance of innate immunity as the first line of defense against infections. It explains the distinction between epithelial barriers, innate immunity, and adaptive immunity, emphasizing the rapid response and specificity of innate immunity. The lecture also touches on the conservation of innate immunity in invertebrates, the cooperation between innate and adaptive immunity in vertebrates, and the various mechanisms and cells involved in the innate immune response.