Marine organisms such as mussels, barnacles, and sandcastle worms demonstrate robust adhesion in aquatic environments. However, the mechanisms underlying their adhesive capabilities remain incompletely understood, and artificial adhesives with comparable performance have yet to be developed. Notably, most of these organisms achieve strong attachment to various underwater substrates through specialized protein-based structures. As a result, researchers have focused on developing peptide- and protein-based underwater adhesives inspired by these natural organisms in recent decades. This review first summarizes the natural protein-mediated underwater adhesive systems of representative marine organisms. It then provides a comprehensive overview of bio-inspired peptide- and protein-based underwater adhesives. Furthermore, the applications of these adhesives across various fields are discussed. Finally, the challenges and opportunities in the development of underwater adhesive biomaterials are briefly explored. © 2025 Elsevier B.V., All rights reserved.