  In this article, we review the current status of $B$-mixing and $b$-hadron
lifetimes both from experimental and theoretical points of view. Furthermore,
we discuss the phenomenological potential of these observables for deepening
our understanding of quantum chromodynamics (QCD) and for indirect searches for
effects beyond the Standard Model (SM). In addition, we present new updated SM
predictions for the mixing observables $\Delta M_{d,s}$, $\Delta \Gamma_{d,s}$
and $a_{fs}^{d,s}$. We conclude with an outlook on future prospects for
theoretical and experimental improvements.
