The research and application of ultra-high-performance concrete (UHPC) have been rapidly developed through the past decade, due to its excellent rheological behaviors, including high workability, excellent durability, and very high compressive strength. This paper reviews the raw materials of UHPC and their role towards optimizing the performance of UHPC. The use of widely available supplementary cementitious materials, such as slag and fly ash for partial replacement of cement and silica fume, can significantly reduce the materials cost without affecting strength. A comparison is presented between the the common cementitious materials in terms of advantages and limitations as well as their optimum use in UHPC. While the fine aggregate has typically the largest particles in the UHPC mix, the coarse aggregate can be successfully introduced into the system of UHPC to further reduce its cost without almost affecting its tensile properties. Since the UHPC typically exhibits very low water to binder ratios, using superplasticizer is very important to ensure the workability to the fresh concrete. Finally, excellent ductility and impact resistance of UHPC are attributed to the use of proper fibers, including steel fibers or carbon fibers due to their superior tensile strengths. The fibers' shape, length, volume content, and orientation can significantly affect the properties of UHPC, and should be carefully optimized.