  The actual limit of the unitarity condition of the first row of the CKM
matrix |V_ud|^2+|V_us|^2+|V_ub|^2=1+\Delta_CKM is \Delta_CKM=-0.0001(6). In
2010 the same was \Delta_CKM=+0.0001(6). Despite the only difference of a sign,
and with an absolute change of the value of one third of the accuracy, a
substantial amount of work has been done in the last two years to improve the
knowledge of all the contributions to this stringent limit to CKM unitarity,
and more is expected in the next years. In this paper we present an organized
summary of all the important contributions presented during the WG1 sessions,
referring as much as possible to the contribution papers prepared by the
individual authors.
