This article provides a detailed discussion of Rotating Biological Disc (RBC) technology in wastewater treatment, a highly efficient, attachment-growth biological process that degrades pollutants through a biofilm formed by microorganisms on a rotating medium. The article elaborates on its operating principles, key components, design considerations, operational advantages (such as simple operation, low energy consumption, and good effluent quality), and potential limitations. It also covers the applications of RBCs in municipal, industrial, and advanced treatment processes, and analyzes common operational challenges and corresponding solutions. Due to its robustness and reliability, RBC plays a vital role in the global wastewater treatment field.