Hadrons containing two heavy quarks provide an ideal benchmark to test effective theories of QCD, thanks to the nonrelativistic behavior of their heavy-quark contents. Nonetheless, 20 years after the discovery of the first exotic heavy meson, X(3872), a comprehensive description of the double-heavy hadron spectrum is still elusive. In this seminar, I discuss how this can be achieved using QCD with static color sources and the diabatic Born-Oppenheimer approximation. In particular, I discuss recent breakthroughs in the treatment of quarkonia, hadronic molecules, and quarkonium hybrids.