Semileptonic hyperon decays

We review the status of hyperon semileptonic decays. The central issue is the V-us element of the CKM matrix, for which we obtain V-us = 0.2250(27). This value is similar in precision to the one derived from K-l3, but higher, and in better agreement with the unitarity requirement, \V-ud\(2) + \V-us\(2) + \V-ub\(2) = 1. We find that the Cabibbo model gives an excellent fit to baryon-beta-decay form-factor data (chi(2) = 2.96 for 3 degrees of freedom) with F + D = 1.2670 +/- 0.0030, F - D = -0.341 +/- 0.016, and no indication of flavor-SU(3)-breaking effects. We indicate the need for more experimental and theoretical work, both on hyperon beta decays and on K-l3 decays.