This study attempts to evaluate the impact of farmland concentration on rural productivity growth within smallholder households in Tanzania. Conceptually, farmland concentration occurs when relatively few farms have relatively large shares of the arable land resources in a given area. If large farms bring benefits that spillover to surrounding smallholders, then we would expect positive impacts of greater land concentration on growth. If, on the other hand, a small set of large farms dominates production, then growth multipliers may be lower than for areas with more egalitarian land distributions.