This chapter focuses on the use of tannins as dietary supplements in dairy cattle nutrition. It begins by first identifying sources of tannins for supplementation, focusing specifically on the tropics and temperate climates. It then moves on to discuss the effects of tannins in dairy cows, such as the effects on palatability, digestion and performance, the use of tannins to mitigate emissions such as nitrogen and methane as well as the effects of tannins on milk quality. The chapter also draws attention to the anthelmintic properties of tannins before moving on to discuss the various factors that can influence the effects of tannin in animals. A section on the onset of tannin effects and long-term efficiency is also provided, which is then followed by an overview of the strategies than can be used to maximise beneficial tannin effects.