The hardness of wheel and rail is one of the main factors that affect the wear of wheel/rail friction pairs. An optimal hardness matching of wheel and rail could play a vital role in reducing the wear and prolonging the service life of wheel and rail. However, at present, there are two kinds of rails matching four kinds of wheels with various hardness in Chinese railway operation, and the material matching behavior becomes complicated. However, regarding the selection and matching of materials and hardness of railway wheel and rail, no uniform and reasonable regulations and standards have been established so far. Besides, with the development of high-speed and heavy-haul railway in China, new damage response has occurred on wheel and rail, which has greatly increased the frequency of wheel repairs, while rail damage behaves slight. Therefore, it is necessary to carry out research on hardness matching of wheel and rail systematically. First, the application situation of wheel and rail materials and their hardness matching across various countries were compared and analyzed in the present work. Through increasing the carbon content, alloying, and heat treatment etc. to refine the pearlite structure, rail materials with good mechanical properties have been developed. The hardness of the R400HT rail can be increased to 400-440HB. Comparing the microstructure of Chinese standard and heat-treated wheel/rail materials, it was found that the hardness and strength increase with the decrease of the ferrite content of wheel and the decrease of the pearlitic lamella spacing of rail. In addition, it is totally different in the selection of wheel and rail materials and hardness in different countries and regions. Specifically, the wheel hardness used in Japan is much higher than rail hardness (HR/HW<1), and the HR/HW value on high-speed railways in Europe is close to 1, while in Chinese high-speed railway, there are many types of wheels and rails with a large hardness range. Secondly, the research progress of hardness matching behaviors of wheel and rail was summarized. Hardness and rail/wheel hardness ratio (HR/HW) definitely have significant effects on wear and rolling contact fatigue damage. Increasing the hardness of the wheels/rails can effectively reduce their wear loss, however, no unified theory has been formed for the impact on the matched rails/wheels. Meanwhile, the results of the optimal wheel/rail hardness matching behavior cannot be intuitively compared, and the previous experience of material selection has not fully applicable to the current railway system, neither. Next, in view of the current hardness matching research of wheel and rail, the potential effects of factors such as work hardening, material microstructure, surface heat treatment process, complex service environment, operating parameters, and other factors (the frequency of wheel/rail, rolling direction, driving and braking conditions, etc.) were discussed. The influence of these factors on the damage and hardness matching behavior of wheel/rail is to affect the work hardening and microstructure by changing the plastic deformation. However, the mechanism of work hardening and microstructure evolution of wheel/rail materials during rolling contact is still unclear. Finally, some prospects for further research were proposed, including establishing a unified and reasonable experimental standard and evaluation system, carrying out the damage behaviors and failure mechanism of high-speed and heavy-haul wheel/rail materials under complex service conditions, research on optimal hardness/toughness matching behaviors and principles and study in high-speed wheel/rail wear law and service life prediction method.