Testing the Standard Model through the CKM Unitarity Triangle requires precise determinations of the magnitude of the relevant quark mixing matrix elements, to match the accuracy of the data from B factories and hadron colliders on the angles. A review of results on s.l. B decays obtained by the LEP Collaborations will be given, with special emphasis on the study of inclusive decays and the determination of the charmless s.l. branching fraction. The status of the extraction of the |V_ub| and |V_cb| elements and the prospects for their averaging with results from exclusive channels and for tests of the underlying theory assuptions will be discussed.