The escalating environmental concerns highlight fears about the sustainability of our planet’s livability. Synthetic polymers, widely used across industries, are major contributors to these issues due to their poor biocompatibility, potential toxicity from degradation, and sustainability challenges in production and disposal. To address these issues, researchers are turning to green biomaterials derived from renewable natural sources, crucial for developing bioactive and biodegradable materials. Among natural polymers, cellulose, chitin, chitosan, and their derivatives stand out in drug delivery systems due to their biocompatibility, biodegradability, accessibility, modifiability, non-toxicity, and stability against environmental factors. Cellulose, abundant in plant cell walls and sourced from various natural origins, offers structural integrity through intermolecular hydrogen bonding. Chitin, found in crustacean shells, and its derivative chitosan, known for its cationic nature and unique properties like antimicrobial activity, they are also prominent. Chemical modifications enhance these biopolymers’ solubility and interactions, enabling their integration into innovative composites. Combining cellulose and chitosan has yielded materials with enhanced functionality, suitable for diverse biomedical applications such as films, aerogels, and membranes. These biopolymer composites exhibit 1D to 3D structures, leveraging cellulose’s hydrophilicity and mechanical strength alongside chitosan’s antimicrobial properties. The growing interest in these sustainable biomaterials stems from their biodegradability and eco-friendliness, offering viable alternatives to conventional petroleum-based products. This chapter provides an overview of cellulose, chitin, and chitosan, discusses their production, and explores recent advancements in their application as green polymers in drug delivery systems, showcasing their potential to address environmental challenges while advancing biomedical technology.