  Motivated by the recent LHCb announcement of a $3.1\sigma$ violation of
lepton-flavor universality in the ratio $R_K=\Gamma(B\to
K\mu^+\mu^-)/\Gamma(B\to K e^+ e^-)$, we present an updated, comprehensive
analysis of the flavor anomalies seen in both neutral-current ($b\to
s\ell^+\ell^-$) and charged-current ($b\to c\tau\bar\nu$) decays of $B$ mesons.
Our study starts from a model-independent effective field-theory approach and
then considers both a simplified model and a UV-complete extension of the
Standard Model featuring a vector leptoquark $U_1$ as the main mediator of the
anomalies. We show that the new LHCb data corroborate the emerging pattern of a
new, predominantly left-handed, semileptonic current-current interaction with a
flavor structure respecting a (minimally) broken $U(2)^5$ flavor symmetry. New
aspects of our analysis include a combined analysis of the semileptonic
operators involving tau leptons, including in particular the important
constraint from $B_s$--$\bar B_s$ mixing, a systematic study of the effects of
right-handed leptoquark couplings and of deviations from minimal
flavor-symmetry breaking, a detailed analysis of various rare $B$-decay modes
which would provide smoking-gun signatures of this non-standard framework (LFV
decays, di-tau modes, and $B\to K^{(*)}\nu\bar\nu$), and finally an updated
analysis of collider bounds on the leptoquark mass and couplings.
