  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.
