Lipids are released in milk as fat globules, which are droplets of apolar lipids surrounded by a complex membrane deriving from the mammary epithelial cell (MEC) and called the Milk Fat Globule Membrane (MFGM). The structure of the MFGM is highly complex and closely related to the mechanisms of milk fat globule secretion in the MEC. Indeed, MFGM is composed of two biological membranes, a phospholipid monolayer deriving from the endoplasmic reticulum and a phospholipid bilayer which originates from the apical plasma membrane of the MEC, with variable amounts of cytoplasm trapped between. We have characterized this complex membrane in several species, including the goat species or camelids. Newly identified MFGM proteins were not only involved in lipid metabolic or exocytosis-related biological processes, but also in cell signaling, translation, or host-defense related mechanisms. Therefore, the milk fat globule should no longer be viewed as an inert structure only devoted to the delivery of lipids to the newborn, but rather as a dynamic and informative compartment which can contribute to improve our comprehension on the mammary gland biology