Weak decays of heavy quarks and leptons

New results on the weak decays of τ leptons and of c and b quarks are described. The HRS Collaboration has presented evidence for a branching ratio of (5.1 ± 1.5)% for the decay, τ minus → pion minus, η meson, τ neutrino. This decay would be possible only if second class currents exist. An upper limit of 1.3% for the same mode reported by the ARGUS Collaboration is in disagreement with this result. The Mark III Collaboration has reported new D0 and D+ branching ratios that reduce the discrepancy between their measurements and earlier ones and largely eliminate the ''charm deficit'' problem in B decay. Recent CLEO and ARGUS measurements of B meson decay modes are reevaluated and discussed using the new D branching ratios. The ARGUS Collaboration has evidence for Bd0 antiBd0 mixing, with τ = 0.21 ± 0.08. This value is much larger than was generally expected