Publisher Summary Langerhans cells are interspersed among keratinocytes which form the “perpetually transient population of the more superficial layers of the epidermis”. They are themselves, therefore, presumably “transients” which continually need replacing. This requires the existence of a parent or stem cell situated at some deeper level which must be continually reproducing itself in order to maintain a “germ-line,” as well as giving rise to a Langerhans cell which is expendable. The nature and significance of the Langerhans cell depends largely on identification of this parent cell. The chapter discusses the demonstration and identification of Langerhans cells by light and electron microscopy, the relationship between between Langerhans cells and melanocytes, and re-evaluation of Langerhans Cell-melanocyte relationship. Langerhans cell has considerable functional importance, is directly or indirectly connected with dermal nerve fibers, and is the division product of a cell located in the dermis. Langerhans cells therefore must be continually migrating across the dermoepidermal junction into the epidermis.