The importance of fit for helmet ensembles is not limited to just comfort. It impacts most other safety and performance needs of the helmets, including helmet retention, and optical and acoustical performance. The addition of optical systems to helmet ensembles increases the need for precision in fit. Helmet systems which were previously acceptable in terms of fit do not necessarily fit well enough to accommodate new performance requirements. The increased need for precision has introduced the need for better definition of human anthropometry for helmet design as well as definition of the head and helmet interface. Traditional anthropometry (human body measurements taken with calipers, or head boards, etc.) is no longer adequate. For advanced helmet systems, data on the shape, or change in the surface curvature and how this relates to helmet systems in three-dimensional space, is now a necessity. In fact, use of the old style of anthropometry can and has created problems rather than resolve them. This paper discusses some of the problems with the old methods and introduces new technologies and research which is being done to address the needs.