The atomistic Green’s function method (AGF) has emerged as a useful tool to study phonon transport across interfaces. A comprehensive review of developments in the AGF method over the last decade is provided in this chapter. The content includes a discussion of the fundamentals of a Green’s function starting from a continuum viewpoint and extending it to the atomistic regime. Comprehensive derivations of the AGF equations (within the harmonic framework) are presented along with intuitive physical explanations for the various matrices involved. The numerical issues in computational implementation of the various mathematical equations are illustrated with a one-dimensional atom chain example. The application of the AGF method to dimensionally mismatched and bulk interfaces and the process of obtaining polarization-specific transmission functions are illustrated with examples. Recent advancements such as integration of the AGF method with other tools (such as density functional theory and Boltzmann transport equation solvers) and extension of the AGF method to include anharmonicity are also presented. Comparisons of results from the AGF method to experimental measurements for superlattice and metal-graphene interfaces are provided.