Around 1998, due to the discovery of renormalon cancellation, it became possible to describe the nature of a heavy quark-antiquark system (such as bottomonium) based on perturbative QCD, both qualitatively and quantitatively. Accordingly, interpretations of the heavy quark mass and interquark force have been modified considerably. I overview what has been understood and theoretical progress since then. For instance, the renormalon dominance picture has been confirmed to be valid and predicts a Coulomb+linear shape of the interquark potential. I also review briefly applications such as high precision determinations of the b,c,t quark masses and alpha_s.