**1. Introduction**

The biology of skin pigmentation plays a critical role in assorted physiological faculties from lower to higher vertebrates, like social interaction, camouflage, mimicry, sexual display as well as distinct racial coloration as seen in human beings. The pigmented biopolymer referred to as melanin is predominant in contributing color to skin, hair, and eyes of mammals. Melanin destined for pigmentation is produced in melanosomes, which are exclusively synthesized within melanocytes and in retinal pigment epithelial (RPE) [1]. Melanocytes are the key components of the pigmentary system because of their ability to produce melanin. These cells are found at many locations throughout the body. Mammalian melanocytes can be classified as "cutaneous" (follicular and epidermal) and "extracutaneous" (e.g., choroidal, cochlear) [2]. Though all of them have derived from pluripotent, NCC and have the capacity to synthesize melanin, their distinct task in all target places are much broader than the melanin synthesis solely.

The existence of melanocytes is not only restricted to the epidermis but they are also found in other locations of the human body such as hair, iris, part of heart, nervous system, inner ear, etc. Here it is important to notice that ability of melanin synthesis is not confined to melanocytes only, but also other cells such as pigmented epithelium of retina, epithelia of iris and ciliary body of the eye, some neurons and adipocytes, which can also generate melanin [3]. Two types of melanocytes have been found: first are the differentiated melanocytes of neural crest origin which are also present at various locations within the body and the other are the RPE cells, originated from the outer layer of the optic cup of brain [4]. The RPE cells perform a critical role in the phagocytosis, that is, turnover and renewal of shed photoreceptor membrane as well as maintenance of normal visual functions [5].

Melanocytes and their production of melanin pigment have important roles in determining the physiology of mammal skin. They synthesize melanin inside a special membrane bound organelle, termed as melanosomes. Melanosomes are transferred via dendrites to surrounding keratinocytes where keratinocytes arrange them to form a critical protective barrier (known as supranuclear "caps") to shield the DNA from UV radiation. The anatomical relationship between keratinocytes and melanocytes is known as "the epidermal melanin unit" and it has been estimated that each melanocyte is in contact with 36 keratinocytes in the basal and suprabasal layers [6].

The amount and type of melanin produced, that is, eumelanin or pheomelanin, as well as its eventual distribution in the epidermis, dramatically affects visible color, which ultimately determines the various functions of the pigment, such as photoprotection. "Normal" pigmen‐ tation is regulated by more than 250 genes and which function during the development, migration, survival, proliferation, and differentiation of melanocytes from their precursors, that is, melanoblasts [7].

The present chapter is proposed to provide morphological and ultra structural details of melanocytes, found in different locations of the body along with their significant functions. Here we will also highlight some miscellaneous functions of melanocytes, other than melanin production. The present chapter will provide significant knowledge on the basics of mamma‐ lian melanocytes from origin to different stages of development along with their specific markers. Signaling pathways of skin melanocytes along with the diseases associated with their disruption have also been elaborated. Concurrently, their etiologies along with the ultrastruc‐ tural details of pigmentary disorders and the role of receptors have also been discussed.
