  An overview is given of the theoretical developments on heavy quarks and
quarkonia in heavy-ion collisions as reported at the "Hard and EM Probes 2018"
conference. Specifically, we address progress in the understanding of
heavy-flavor diffusion and its hadronization, quarkonium transport and the
extraction of quarkonium melting temperatures, energy loss of heavy quarks at
high momentum, and their rescattering in small colliding systems.
