In this chapter, we present an outline of the information available on major indigenous phospholipid membrane-associated milk enzymes. Only enzymes the presence of which have firmly been documented are considered, except catalase. A large number of enzymes have previously been associated with milk phospholipid membranes, but many of these are omitted, because they are judged to have low abundance, to be contaminants, to be inactive, or to have limited significance in milk. Information about enzyme presence, activity measurement, structure, isolation, biological role and significance in milk is presented.