Casein molecules are used in food industry as ingredients. They can be used as isolated forms and under micellar form consisting in an association of different casein molecules and calcium phosphate. In this review, after a brief reminder of the main characteristics of casein molecules and casein micelles, the modifications of caseins induced by physical, chemical, and enzymatic actions are reported. The resulting new physicochemical properties (mineral and casein compositions, charge, hydrophobicity, aggregation state, and morphology) and techno-functionalities (heat stability, viscosity, gelation, emulsifying, and foaming properties) are described and discussed with a special attention paid to the results obtained in our laboratory since several decades.