This review discusses the methods for recovering chitin from marine organisms, focusing on both enzymatic and chemical treatments for deproteinization and demineralization. It also examines the conditions for chitosan preparation, emphasizing the impact of varying degrees of acetylation (DA) and molecular weight (MW) on the synthesis. The main characterization techniques for chitin and chitosan are reviewed, highlighting the role of solubility in relation to chemical structure, particularly the distribution of acetyl groups. Biological activities such as antibacterial, antifungal, antitumor, and antioxidant properties are presented, with a focus on the relationship between chemical structure and biological activity. The review concludes by discussing several pharmaceutical and biomedical applications of chitin and chitosan, emphasizing their biocompatibility and biodegradability.This review discusses the methods for recovering chitin from marine organisms, focusing on both enzymatic and chemical treatments for deproteinization and demineralization. It also examines the conditions for chitosan preparation, emphasizing the impact of varying degrees of acetylation (DA) and molecular weight (MW) on the synthesis. The main characterization techniques for chitin and chitosan are reviewed, highlighting the role of solubility in relation to chemical structure, particularly the distribution of acetyl groups. Biological activities such as antibacterial, antifungal, antitumor, and antioxidant properties are presented, with a focus on the relationship between chemical structure and biological activity. The review concludes by discussing several pharmaceutical and biomedical applications of chitin and chitosan, emphasizing their biocompatibility and biodegradability.