Because of the apparent slowdown in the growth of crop yield potential, the increasing share of farmers already using modern crop varieties, and the accelerating flow of knowledge on agricultural technology, one would expect to find gradual convergence in observed crop yields. Instead, using a new, sub-national yield database, we find a divergence. We illustrate how technology generation has been biased towards more-favored production systems, leaving persistent pockets of low yields in more marginal lands. Rainfall patterns appear to have changed in ways that exacerbate yield divergence. Cross-border barriers to technology spillover appear larger among than within countries