Theoretical Aspects of Heavy Flavour Physics

I review the status of theoretical aspects of B-decays. The principal difficulty in interpreting the wealth of experimental data is the control of non-perturbative QCD effects, and the talk is focused on attempts to control these effects. Lattice results for the decay constants, B-$\bar B$ mixing and semileptonic form-factors are summarized. The discrepancy of the theoretical predictions and experimental measurements for the ratio of lifetimes $\tau(\Lambda_b)/\tau(B_0)$ is discussed, as well as the status of the semileptonic branching ratio of the B-meson. The difficulties in making quantitative predictions for exclusive nonleptonic decays are stressed, and some recent approaches to this problem are outlined.