The threat of anthelmintic resistance has loomed over recommendations to control gastrointestinal nematodes (GIN) in sheep for several decades, and in some regions GIN is threatening the sustainability of sheep farming. This chapter describes the current state of options to achieve sustainable control of GIN in sheep, covering general principles of worm control and methods specific to controlling GIN, including nematophagous fungi, condensed tannins, copper oxide wire particles and vaccines.