**5. Summary**

Researches of bulk high-entropy ceramic have been reported on metal oxides, refractory carbides, borides, and silicides. HECs with homogenous single-phase structure reveal superior mechanical performance and additional properties like thermal-electrical property of high-entropy oxides. Most scientific effort has been put in exploring various fabrication methods, characterizing the high-entropy structure and the remarkable physical and chemical properties. However, to fully understand HECs that involves a complex multicomponent ceramic system, the problem remains: what are the most significant phase formation rules in a HECs material? How can the potential applications of HECs be realized? A more systematic investigation of the material selection rules that already exists in a metallic high-entropy system is highly demanded in the ceramic system in order to optimize the material design and processing work.

The reported research in the past 10 years on high-entropy ceramic coatings has shown development of coatings with exceptional mechanical, high temperature, electrical, corrosion, and wear-resistant properties. High-entropy ceramic coatings have great potential in different applications, such as wear and corrosion resistant coatings, thermal barrier coatings, and electrical and biomedical applications. The control on variation of deposition parameters can be advantageous in achieving coating with extremely high strength values and highly densified structures, which can be corrosion resistant and biocompatible. Future work on development of nanocomposite and multilayer high-entropy ceramic coatings can possess super hardness properties. Furthermore, high temperature corrosion, mechanical, and tribological properties of high-entropy ceramic coatings need to be addressed.
