Yann Chalopin Centre National de la Recherche Scientifique (CNRS) The aim of this talk is to introduce the transport of thermal energy from a microscopic picture. We will notably discuss the radiative and conductive properties of different classes of nanomaterials by demonstrating that heat exchanges in condensed matter can be probed by looking at the momentum and displacement fluctuations of atomic nucleus. This will allow us to introduce a numerical method known as the molecular dynamics. An overview of the technique will be presented and illustrated with specific examples to demonstrate how it can be used to investigate thermal physics at short scales.