The design of case-hardened components is an iterative process, requiring the consideration of multiple interrelated factors. This chapter walks readers through the steps involved in selecting an appropriate material and assessing the influence of alloy composition and cooling rate on core properties including hardenability, microstructure, tensile and yield strength, ductility, toughness, and fatigue resistance. It likewise explains how carbon affects case hardenability, surface hardness, and case toughness and how case depth influences residual stresses and bending and contact fatigue. It also discusses the effect of quenching methods and addresses the issue of distortion.