Hyperon Semileptonic Decays and CKM Unitarity

We perform a new numerical analysis of hyperon semileptonic decays emphasizing the systematic uncertainties. The poor understanding of SU(3) symmetry breaking effects at second order in the vector form factor translates into a large error of |Vus|. Using our determination |Vus|=0.226±0.005 together with those coming from other sources we test the unitarity of the CKM matrix.