Theory of Semi-- and Nonleptonic Decays of Heavy Mesons

I review some of the recent developments in the theoretical description of weak inclusive decays of heavy mesons. The topics cover the value of $|V_{cb}|$ as extracted from semileptonic inclusive decays and a short discussion of the theoretical errors. I also present the results of a recent calculation of next--to--leading order corrections to nonleptonic inclusive B decays which allows an improved prediction of the semileptonic branching ratio of B mesons.