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 chan
ge 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.
