The first five articles in this issue are based on presentations given at the 1st International Symposium on Surface Hardening of Stainless Steels, held October 22-23, 2007 at Case Western Reserve University (Cleveland, OH). An international audience of over 100 conferees attended the symposium, which covered low-temperature processes for surface hardening of stainless steels by ''colossal'' concentrations of interstitial solutes. Presentation topics included process development; microstructural characterization; performance evaluations (including mechanical behavior, and fatigue, wear, and corrosion resistance); and examples of commercial application.Expanded austenite, or S phase, has been a focus of much research for the past two decades in the United States, Europe, and Japan. This phase is a supersaturated solid solution, case-hardened layer, usually 10-to 50-lm thick, achieved by diffusion of carbon or nitrogen interstitially into an austenite matrix. This phase can be achieved on chromium-containing alloys not commonly considered hardenable by heat treatment, such as austenitic stainless steels.Processes to achieve this case layer must first remove the naturally occurring passive layer that forms on these alloys. To avoid the nucleation and growth of surface carbides or nitrides, these processes are performed at relatively low temperatures, usually below 500°C. Several technologies have demonstrated similar results, including gas phase processes, ion or plasma processes, and even salt bath processes. A few commercial entities now provide lowtemperature surface treatments of austenitic alloys, using carbon, nitrogen, or a combination of the two as the interstitial hardening element.The diffusional layer created by these processes has a very high surface concentration of carbon (measured at up to 12 at. pct) or nitrogen (up to 37 at. pct), resulting in ''superhard'' surfaces-values of 1200 to 1400 HV-and compressive residual stresses that can exceed 3 GPa. The effect on the performance characteristics of treated surfaces is astounding, with significant improvements in fatigue life and wear resistance, as well as a remarkable enhancement of corrosion resistance in chloride-containing environments. Research is continuing on all these topics, and this emerging surface engineering technology continues to be a fruitful area of scientific and commercial interest. A second symposium is planned for May 2010 in Cleveland.