The article examines gender differences in agricultural productivity using panel data for Tanzania. At the national level, there is weak evidence of mean differences in productivity between male and female plots, but conditional on manager characteristics, plot characteristics, inputs, and crop choice, plots managed solely by a woman are consistently found less productive than all other plots. An Oaxaca-Blinder-type decomposition reveals that important factors explaining the gender differential are plot area and family labor. Women are able to obtain higher yields on smaller plots farmed with less male labor and more female labor and thus cover the gender gap in productivity at the aggregate level, but there are still significant unobservable factors which contribute to widening the gap.