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This paper reviews the basic concepts of rays, ray tracing algorithms, and radio propagation modeling using ray tracing methods. We focus on the fundamental concepts and the development of practical ray tracing algorithms. The most recent progress and a future perspective of ray tracing are also discussed. We envision propagation modeling in the near future as an intelligent, accurate, and real-time system in which ray tracing plays an important role. This review is especially useful for experts who are developing new ray tracing algorithms to enhance modeling accuracy and improve computational speed.