Breast milk is a biological fluid which provides the vital nutrition and immunity for the neonate and infant. Only a very few investigations of the cellular organisation and functioning of the normal lactating breast have been done since Sir Astley Cooper performed detailed dissections of the breast more than 160 years ago. Little is known about the physiology of the mechanisms described for transport of proteins, lipids, ions, nutrients and water into milk by which certain drugs and even toxic substances enter milk or mammary gland. Knowledge of these processes is important to the physician and to researchers as well. Therefore, in this short communication, we intend briefly highlighting the current understanding of the normal solute transport and secretory processes involved in milk production. Solutes can enter milk through both transcellular and paracellular routes. We describe the exocytotic pathway, lipid secretion pathway, transcytosis pathway, membrane transport pathway and the paracellular pathway and briefly address the complexity involved due to the number of systems involved in solute transport in the lactating breast and the potential for cross-talk between hormones and regulatory mechanisms.