A brief overview of the theory of open heavy flavor dynamics in QCD matter produced in high energy heavy-ion collisions is presented. First, we will summarise the phenomenological efforts to estimate the heavy quark diffusion coefficients obtained within different models. Then, the recent theoretical developments from different groups to probe the medium properties using heavy quarks will be presented. Heavy quarks are also considered as an ideal probe for the initial stage of heavy-ion collisions. In the end, we present the recent theoretical progress made to probe the early-stage effects, pre-equilibrium phase, and electromagnetic fields.