New results on semileptonic b decays from LHCb

We report new measurements, based on the Run I dataset collected by the LHCb experiment, of the B0 mixing frequency Dm_d and the CKM matrix element |V_ub| using semileptonic b decays. The former is the most precise measurement ever performed; the latter represents the first determination of |V_ub| using a baryonic decay, and adds an important constraint on a possible explanation for the discrepancy between exclusive and inclusive determinations of this observable.