Surface functionalization via molecular design has been a key approach to incorporate new functionalities into existing biomaterials for biomedical application. Mussel-inspired polydopamine (PDA) has aroused great interest as a new route to the functionalization of biomaterials, due to its simplicity and material independency in deposition, favorable interactions with cells, and strong reactivity for secondary functionalization. Herein, this review attempts to highlight the recent findings and progress of PDA in bio-surface functionalization for biomedical applications. The efforts made to elucidate the polymerization mechanism, PDA structure, and the preparation parameters have been discussed. Interactions between PDA coatings and the various cell types involved in different biomedical applications including general cell adhesion, bone regeneration, blood compatibility, and antimicrobial activity have also been highlighted. A brief discussion of post-functionalization of PDA and nanostructured PDA is also provided.