Milk fat physical properties, including its crystallization and melting properties, are involved in many food applications (cream, butter, cheese, and also in bakery). Over a wide range of temperatures, milk fat is a mixture of solid crystals connected in networks and embeded in a liquid phase. These crystals evolve, as a function of temperature and temperings, in terms of amount, composition and structural characteristics. This book chapter describes the crystallization properties and polymorphism of milk fat and shows how they are affected by (1) the dispersion state, i.e. anhydrous fat versus emulsified fat dispersed in numerous droplets, (2) the cooling rates and temperings, (3) shear applied during processing, (4) the presence of minor lipid compounds (FFAs, MAGs, DAGs, phospholipids), (5) the fatty acid and triacylglycerol (TAG) compositions, including milk fat from various species (human, goat, dromedary milks). Deciphering the crystallization properties of milk fat requires investigations at different scale levels, recordings as a function of temperature and time, and the combination of physical techniques. Increasing knowledge in the area of TAG crystallization yields fascinating new insights that contribute in increasing further the value of milk fat in food applications.