Functional oligosaccharides (FOs), derived from the processing wastes of fruits and vegetables, present a valuable opportunity for sustainable by-product development. These oligosaccharides, which include fructooligosaccharides (FOS), galactooligosaccharides (GOS), and pectic oligosaccharides (POS), are collectively known for their prebiotic properties. The prebiotic properties enhance gut health by promoting beneficial microorganisms in the gut microbiota. This chapter explores the extraction and analysis of FOs from agri-food residues, such as peels, pulps, and pomace. The use of physical processes (e.g., hydrothermal processing), chemical processes (e.g., acid hydrolysis), and enzymatic methods will be explored. The incorporation of such oligosaccharides into food products can enhance nutritional value and offer health benefits, addressing both waste management issues and consumer demand for functional foods. Moreover, the valorization of fruit and vegetable processing by-products into FOs aligns with and contributes to sustainability in the food industry. So, this chapter focuses on the extraction of FOs and identification of compounds. This will be of great help to B.Tech., M.Tech., B.Sc., and M.Sc. students, research scholars, and faculty members.