Feed efficiency, as defined by the fraction of feed energy captured in products, has more than doubled for the US dairy industry in the past 100 years. This increased feed efficiency resulted from increased milk production per cow achieved through genetics, nutrition, and management with the desired goal being greater profitability. With increased milk production per cow, more feed is consumed per cow but a greater portion of the feed is partitioned toward milk instead of maintenance and body growth. The dilution of maintenance has been the overwhelming driver of enhanced feed efficiency in the past, but its impact diminishes with each successive increment in production relative to body size. In the future, we must focus on new ways to enhance digestive and metabolic efficiency. One way to examine variation in efficiency among animals is residual feed intake (RFI), a measure of efficiency that is independent of the dilution of maintenance. Cows that convert feed energy to net energy more efficiently, or have lower maintenance requirements than expected based on BW, use less feed than expected and thus have lower RFI. Cows with low RFI likely digest and metabolize nutrients more efficiently and should have overall greater efficiency and profitability if they are also healthy, fertile, and produce at a high multiple of maintenance. Genomic technologies will help to identify these animals for selection programs. Nutrition and management also will continue to play a major role in farm-level feed efficiency. Helping all farms achieve the efficiency of the best farms would have a major effect on feed efficiency for the industry. Management practices such as TMR-feeding and grouping improve rumen function and efficiency, but they have decreased our attention on individual cows. Perhaps new computer-driven technologies will enable us to optimize efficiency for each individual cow within a herd, or to optimize animal selection to match management environments. In the future, availability of feed resources may shift as competition for land increases. New approaches combining genetic, nutrition, and other management practices will help optimize feed efficiency, environmental sustainability, and profitability.