In this chapter, the authors overview the cumulant solution to light propagation in a turbid medium and its applications in deep imaging beyond the diffusion equation. They help readers to grasp the key features of the cumulant solution to radiative transfer equation (RTE) and appreciate the power of this Cumulant method from some salient diverse applications in biophotonics and remote sensing. The cumulant solution to RTE has been successfully applied in optical imaging beyond the diffusion approximation, for example, constructing a transport forward model for optical imaging, cloud remote sensing, and early photon tomography for imaging. The authors review the analytical solution of the time-dependent RTE in an infinite uniform medium with an arbitrary light scattering phase function using cumulant expansion and some applications in imaging with multiply scattered light beyond the diffusion approximation.