Linseed (or flaxseed) (Linum usitatissimum) co-products, derived from the processing for oil or other industrial purposes, offer significant potential as alternative feed ingredients in animal nutrition. This chapter explores the importance of linseed in livestock feeding, emphasizing its rich nutrient profile. This chapter provides a detailed overview of linseed co-products, such as linseed meal, linseed cake, and other derivatives, highlighting their nutritional composition, variability, and potential applications across ruminants, swine, and poultry. The chapter also discusses the challenges and limitations in utilizing linseed co-products as well as the practical strategies for incorporating these co-products into livestock diet, with a focus on processing technologies to optimize digestibility and safety. Furthermore, the environmental and sustainability implications of linseed co-product valorization are examined, positioning them as valuable contributors to sustainable agriculture. Finally, the chapter outlines future perspectives, emphasizing the need for research to optimize production, enhance product consistency, and expand applications.