We present a brief overview of the theory of open heavy flavor dynamics in the QCD medium created in high-energy heavy-ion collisions. The ongoing phenomenological efforts to determine the heavy quark diffusion coefficients in the quark-gluon plasma (QGP) are summarized. Additionally, recent theoretical advancements by various groups in utilizing heavy quarks to probe medium properties and hadronization mechanisms are discussed. We highlight recent progress in investigating the pre-equilibrium phase and the effects of electromagnetic fields.