  All existing "positive" results on two neutrino double beta decay in
different nuclei were analyzed. Using the procedure recommended by the Particle
Data Group, weighted average values for half-lives of $^{48}$Ca, $^{76}$Ge,
$^{82}$Se, $^{96}$Zr, $^{100}$Mo, $^{100}$Mo - $^{100}$Ru ($0^+_1$),
$^{116}$Cd, $^{130}$Te, $^{150}$Nd, $^{150}$Nd - $^{150}$Sm($0^+_1$) and
$^{238}$U were obtained. Existing geochemical data were analyzed and
recommended values for half-lives of $^{128}$Te, $^{130}$Te and $^{130}$Ba are
proposed. Given the measured half-life values, nuclear matrix elements were
calculated. I recommend the use of these results as the most currently reliable
values for the half-lives and nuclear matrix elements.
