Enhancing the fat content of lactation diets is a convenient means to raise dietary energy-density and intake, which in turn helps support the heightened energy demands of modern high-producing dairy cows. Fat-feeding is a useful strategy to limit excessive feeding of highly fermentable carbohydrates (i.e., high-starch feeds), thus reducing the risk of sub-acute acidosis and milk fat depression (MFD). Although fat feeding can be advantageous for the above-mentioned reasons, its use in lactation diets is constrained by adverse effects on dry matter intake at high feeding levels (≥7 percent of ration dry matter), limits associated with feeding rumen-degradable unsaturated fat (i.e., oils that contribute to MFD), and cost of commercial fats. Producers and nutritionists need to carefully consider the type, composition, and feeding level of fat to leverage the advantages of this source of dietary energy, while maximizing their cost-effectiveness in changing market conditions.