Rising environmental concerns associated with the depletion of nonrenewable resources and the accumulation of persistent waste are fueling increased interest in biodegradable marine biopolymers as sustainable alternatives. Marine polysaccharides represent a diverse class of natural biopolymers derived from marine animals, seaweeds, and microorganisms, offering immense potential in food processing and preservation. This chapter presents a comprehensive overview of their sources and classification, highlighting key examples such as chitosan and chitin from crustaceans, alginate and carrageenan from seaweeds, and gellan and xanthan gum from marine microbes. The structural and chemical properties of these polysaccharides are discussed in detail, including their molecular architectures, glycosidic linkages, functional group modifications such as acetylation and sulfation, net charge, molecular weight, and conformational flexibility, all of which influence their behavior in food systems. The chapter also explores the wide-ranging applications of marine-derived polysaccharides in food processing. These include their roles in developing gluten-free products, encapsulating nutrients and flavors, modifying texture, and enabling the production of low-fat and low-calorie foods. Their contribution to food preservation is equally significant, particularly due to their antimicrobial and antioxidant properties, as well as their use in edible films and coatings that extend the shelf life of perishables. Finally, the chapter outlines emerging trends and future perspectives, emphasizing sustainable extraction technologies and novel formulation strategies that position marine polysaccharides as key enablers in advancing health-focused and eco-friendly food innovations.