In Chapter 3, the improved geometric optics method based on electromagnetic integral relations is introduced. Both the surface/volume integral equations linking the near field on the particle surface/volume internal field to the far field are derived. A proof is presented to show the equivalence of the surface and volume integral equations. The surface (or volume) integral equation is then employed to map the near field computed by the geometric optics method to the far field. To improve the computational efficiency of the mapping of the near field to the far field as well as ray tracing, a broad-beam method is presented. A beam-splitting technique based on computer graphics is presented to facilitate efficient beam tracing processes. The performance of PGOM is evaluated via comparing the PGOM simulations and the benchmarks provided by the invariant-imbedding T-matrix method (IITM). Furthermore, a simplified physical-geometric optics method, which considers the interference of emerging waves through the “ray-spreading effect,” is illustrated. A number of examples for the physical-geometric optics method and its simplified version are presented. Finally, this chapter presents a synergistically unified method based on a combination of IITM for small-to-moderate size parameters and PGOM for moderate-to-large size parameters.