Milk fat constitutes up to 30% of the milk dry weight, carries 50% of the energy and contains essential water-insoluble vitamins. It is solubilized in the milk in complex fat globules. The majority of milk fat consists of fatty acids esterified to triglycerides. There is a considerable plasticity of ruminant milk fatty acid composition. Special attention will be given to fatty acids that play an important role in human health. These include saturated fatty acids, oleic acid (18:1 n-9), n-6, or n-3 types of C18:2 to C22 polyunsaturated fatty acids, trans isomers of C18:1 and C18:2, and isomers of conjugated linoleic acid (CLA). Milk and dairy products are a major source of 12:0, 14:0, 16:0, and trans fatty acids in the human diet. Consequently, there is considerable interest in the altering process of milk fatty acid composition with the overall aim of improving the long-term health of consumers. Important targets include the decrease of certain medium-chain saturated cis fatty acids to reduce cardiovascular risks. Furthermore, an increase of defined trans fatty acids which have been shown to exert anti-carcinogenic properties in a range of human cell lines and animal models are desired. Manipulation of milk fat content, and its fatty acid composition, through breeding and nutrition strategies have been important targets for the dairy industry in many parts of the world. Despite the advanced research on the effects of dietary factors on the sensorial quality of milk and diary products, more research is needed to evaluate in more detail how different feeding strategies lead to a change of the nutritional, sensorial, and technological aspects of milk fat quality.