The use of pasture grazing systems offers a means to improve feed self-sufficiency and reduce labor for dairy farmers. Consumers also are interested in milk and dairy products obtained from cows on pasture-based diets. However, little is known about the difference between milk obtained from grazing cows and general milk obtained from cows on an indoor feeding system. There is almost no information about the flavor constituents, whereas many studies have been conducted on such characteristics as the fatty acid composition, conjugated linoleic acids, and carotenoids of milk from grazing cows. In this review, we describe studies that have characterized the volatile organic compounds (VOCs) in milk and our investigations on the effects of pasture intake on VOCs in milk. The VOC, 1-phytene has been used to characterize milk from grazing cows as there is a strong positive correlation between pasture intake and the concentration of 1-phytene in milk. In addition, milk from cows in a grazing system can be distinguished from that of animals in an indoor feeding system using the levels of 1-phytene, γ-dodecalactone, 2-phytene, neophytadiene, and δ-dodecalactone.