Fucoidan, a sulfated polysaccharide predominantly derived from brown algae, has garnered significant research interest due to its diverse biological activities and potential biomedical applications. This review systematically examines both established and novel extraction methods for fucoidan. Traditional techniques, including hot water, acid, and alkaline extraction, are summarized, alongside emerging approaches such as enzymatic hydrolysis, ultrasound-assisted, microwave-assisted, and subcritical water extraction, which demonstrate enhanced efficiency and yield. The paper further synthesizes the extensive research on the compound's multifaceted physiological functions, highlighting its immunomodulatory, anti-tumor, antioxidant, anticoagulant, lipid-lowering, and antiviral properties. These findings collectively underscore the critical relationship between fucoidan's structural characteristics—influenced by its monosaccharide composition, molecular weight, and sulfation pattern—and its resultant bioactivities. The conclusion affirms fucoidan's substantial value and broad applicability, particularly within the biomedical sector, for advancing health and therapeutic strategies.