  We review many lattice QCD calculations that impact the precise determination
of the CKM matrix. We focus on decay constants and semileptonic form factors of
both light ($\pi$ and K) and heavy-light ($D_{(s)}$ and $B_{(s)}$) mesons.
Implication of $\Lambda_b$ form factors will be shown. When combined with
experimental results for branching fractions and differential decay rates, the
above calculations strongly constrain the first two rows of the CKM matrix. We
discuss a long standing difference between $|V_{ub}|$ and $|V_{cb}|$ as
determined from exclusive or inclusive decays.
