Nitinol (an acronym for the Nickel-Titanium Naval Ordnance Laboratory) has been extensively explored as an implant material for the medical industry. The potential problem with Nitinol implant devices is the release of Ni in the human body, which has stimulated a great deal of research on surface modifications and the application of coatings. This paper presents a comprehensive review of various treatments to modify the surface of Nitinol in an effort to inhibit Ni release and to render improved biocompatibility. We discuss the important in-service properties of Nitinol, such as biocompatibility, corrosion resistance, stability, uniformity, and the nature of passivating oxides produced by passivation, electropolishing, magnetoelectropolishing, ion beam implantation, sterilization, and artificial coatings.