Skin color and photoprotection depend on two epidermal cell types, melanocytes and keratinocytes. Melanocytes are the melanin pigment-producing cells and form a unique membrane-enclosed organelle, called the melanosome, in which melanin is synthesized, stored and ultimately transferred to keratinocytes. The biogenesis and function of the pigmented melanosome relies on membrane trafficking pathways, some of which are targeted in the Hermansky-Pudlak Syndromes (HPS) – a group of rare genetic disorders characterized by oculocutaneous albinism, excessive bleeding, and other systemic defects. Most of the genes that are mutated in HPS patients encode protein subunits of molecular complexes called BLOCs that play some roles in regulating trafficking pathways. However, the cellular and molecular functions of the BLOCs remain poorly understood. I will discuss here some of our recent studies illustrating how the BLOCs, particularly BLOC-1 and its partners, control membrane trafficking events in and out of the melanosomes. A better understanding of the cell biology of BLOCs elucidates how their malfunction leads to melanosome dysfunction in HPS, and could identify potential novel gene candidates targeted in uncharacterized forms of this syndrome.