Differences in technology levels across countries account for a large component of the differences in wages and per-capita GDP across countries worldwide. This article reviews micro studies of the adoption of new technologies and the use of inputs complementary with new technologies to shed light on the barriers to technology diffusion in low-income countries. Among the factors examined affecting decisions pertaining to technology choice and input allocations are the financial and nonfinancial returns to adoption, one's own learning and social learning, technological externalities, scale economies, schooling, credit constraints, risk and incomplete insurance, and departures from behavioral rules implied by simple models of rationality.