Agro-industrial waste, produced in substantial volumes across the global food and agricultural sectors, presents both an environmental burden and an opportunity for resource recovery. This chapter explores the valorization of these residues into a diverse range of high-value bioproducts, including biofuels, bioactive compounds, bioplastics, natural aromas, and pigments. Emphasizing sustainable biotechnological and chemical processes, the chapter details how lignocellulosic biomass, fruit and vegetable by-products, and other organic waste streams can be converted through microbial fermentation, enzymatic hydrolysis, and thermochemical methods. By integrating circular economy principles, agro-industrial waste valorization offers a promising pathway toward resource efficiency, environmental sustainability, and the development of innovative bio-based products.