Hard partonic jets that are produced from early stage scatterings provide an important tool for studying the properties of the quark-gluon plasma created in high energy nuclear collisions. During their propagation through the hot and dense nuclear matter, the interactions of hard jets with the medium usually lead to parton energy loss. This is commonly referred to as jet modification or jet quenching. In this talk, I will discuss the current status of parton energy loss and jet modification studies in relativistic nucleus-nucleus collisions. I will also talk about our studies of the evolution dynamics of open heavy flavors produced in heavy-ion collisions.