This chapter provides a comprehensive review of the use of algae, encompassing both microalgae and seaweeds, in sustainable livestock production systems. Algae exhibit high nutrient density, offering protein, essential fatty acids, and a variety of bioactive compounds that can partially replace conventional feed crops such as soy and maize, thereby mitigating land-use pressures and reducing environmental footprints. Interestingly, certain macroalgae, such as Asparagopsis taxiformis, have been shown to reduce methane emissions in ruminants by interfering with methanogenic pathways, thus aligning with current strategies for greenhouse gas mitigation. This chapter examines algae-derived feeds’ nutritional, functional, and environmental benefits across monogastric, ruminant, and aquaculture systems. It incorporates a detailed comparative analysis that highlights the complementary roles of microalgae and seaweeds: microalgae deliver concentrated proteins and lipids along with antioxidants, while seaweeds contribute essential minerals, complex polysaccharides, and dietary fibers that promote gut health. Moreover, this chapter situates algae production within circular bioeconomy frameworks, emphasizing their roles in carbon sequestration, nutrient recycling, and efficient utilization of marine and wastewater resources. Despite these advantages, challenges persist regarding cost-effective large-scale cultivation, processing, and feed formulation, as well as the need for standardized regulatory frameworks. Addressing these issues will be critical to fully harnessing the potential of algae in reducing environmental impacts and enhancing livestock productivity, particularly in regions limited by freshwater or arable land. The findings underscore the viability of algae-based feeds as a strategic component in achieving global food security and environmental sustainability.