ChitosanChitosan is a probable biopolymer that is derived from chitin, which is generally recoverable from seafood waste, i.e., from the shells of shrimp and crab. The current chapter provides an in-depth overview of chitosanChitosan extraction techniques from marine wasteMarine wastes, with a focus on traditional methods and new green processes to reduce environmental impactEnvironmental impact and enhance product quality. It also analyses the chemical and physical properties of the obtained chitosanChitosan and how these make it suitable for bio-based applications. The chapter focuses on the pharmaceutical uses of chitosanChitosan-based materials, including drug delivery systems, improved bioavailability, and the formulation of topical products, as well as their medical applications, such as wound dressings, tissue engineering, and antimicrobial agents. It also considers the future potential and challenges of enhancing the application of chitosanChitosan in medicine, following the “waste-to-value” philosophy, for the benefit of sustainable innovation and the circular economyCircular Economy (CE).