This lecture covers the Monte Carlo method applied to thermal radiation, focusing on radiative energy transfer in participating media. The instructor begins with a recap of previous exact solutions for simple systems, particularly in one-dimensional geometries involving black and gray walls. The lecture emphasizes the importance of understanding radiative exchange and the statistical nature of the Monte Carlo method, where bundles of photons are tracked to calculate radiative flux and energy transfer. The instructor explains how to define random bundles, follow their paths, and analyze their interactions with surfaces and media. Key concepts such as radiative equilibrium, emission, absorption, and scattering are discussed, along with their mathematical formulations. The lecture also includes practical examples, demonstrating how to compute net radiative heat flux between walls and the temperature distribution in a medium. The instructor highlights the significance of these methods in complex thermal systems, providing insights into the behavior of radiative heat transfer in various scenarios.