Establishing a complete picture of phonon dispersions and mean-free-paths is important to understand the microscopic characterization of phonon transport, and design an efficient thermoelectric compound. As a very useful tool, the neutron scattering technique can not only map phonon dispersions, but also the lifetimes across the entire Brillouin zone. These measurements provide key insights about phonon scattering mechanisms, such as phonon anharmonicity, and scattering by point defects or nanostructures. Furthermore, the first-principles simulations of atomic dynamics are performed. We present the results from the studies of several important thermoelectric materials, PbTe, SnTe, and AgSbTe2, and illustrate how this integrated approach can be used to reach a new level of understanding of the thermal conductivity.