The theoretical aspects of the gravitational motion and radiation of binary black hole systems are reviewed. Several of these theoretical aspects (high-order post-Newtonian equations of motion, high-order post-Newtonian gravitational-wave emission formulas, Effective-One-Body formalism, Numerical-Relativity simulations) have played a significant role in allowing one to compute the 250 000 gravitational-wave templates that were used for searching and analyzing the first gravitational-wave events from coalescing binary black holes recently reported by the LIGO-Virgo collaboration.