Economic development is often associated with the adoption of new technologies. The three chapters in this dissertation ask how societies can achieve efficient adoption of these technologies. The first two chapters analyze the dramatic spread of a new communication technology---the mobile phone---in the East African country of Rwanda, using transaction data. Many technologies important for the modern economy are network goods; these goods tend to diffuse inefficiently in the absence of careful policy design. The first chapter introduces a new method to estimate the value of a network good, and to simulate the effects of policies. Economic actors also must decide whether a given technology is worth adopting. The second chapter analyzes how individuals learn about a new technology, by tracing the adoption of a new, cheaper mobile phone plan. The third chapter considers the side effects of new technologies, specifically, how innovation affects dimensions of quality that are not observed by consumers. / Economics