Abstract: There are various interfacial phenomenona in ironmaking and steelmaking, including slag foaming, nucleation, aggregation, removal of inclusions in steel, and refractory corrosion. The slag-metal interface has a crucial influence on the mass transfer, energy transfer, and interfacial chemical reaction. Interfacial wettability is a very important aspect of the interfacial interaction, and studying it is essential to further understand the interfacial phenomenona. In general, the interfacial wettability can be measured by contact angle and interfacial tension. In studying interfacial phenomena, it is necessary to first measure various quantities of interfacial wettability such as surface tension, interfacial tension, and contact angle, on the same conditions of interfacial phenomena or processes. Improving the interfacial wettability can be beneficial to the control of melting and refining processes. For example, when the contact angle between the molten slag and inclusion in steel reduces and the surface tension of the molten slag increases, the adhesion between the molten slag and inclusion is stronger, and it becomes easier to remove the inclusions. Therefore, the basic concepts of contact angle and interfacial tension were first introduced in this paper. Furthermore, the common methods of measuring contact angle and surface tension in an elevated temperature system were summarized, especially for the sessile drop method, which is the mostly used in laboratory experiments. During steelmaking processes, the interfacial wettability is significantly influenced by the system compositions, especially the surface active elements in steel and the surface active composition in slag. Moreover, the influences of temperature are also considerable. Hence, the effects of these two main factors, compositions and temperature, on the interfacial wettability were analyzed in detail. Finally, the wettability among the common materials in steelmaking processes was summarized.