This book describes the details of the research and development of nickel-saving high nitrogen austenitic stainless steel and high nitrogen steel (HNS) with excellent corrosion resistance in the sea. This resistance was realized by using nitrogen (N), one of the ubiquitous elements, as an alloying element. By using N it is possible to save nickel (Ni), a national strategic substance in Japan, to be partially reduced or to be totally free. Not only basic information about low nickel HNS but also its promising application to bipolar plates of solid polymer fuel cells are provided. Reduction of Ni ions in the cell environment can be expected to extend the life of the fuel cell. Furthermore, there is discussion of the serendipitous application and impact of nickel-free HNS in the field of biomaterials as an anti-nickel allergy material, leading to its development for coronary stents.