This empirical study examines the economic impact of fixed and mobile broadband in the least developed countries (LDCs), landlocked developing countries (LLDCs) and small island developing states (SIDS). These 91 most vulnerable countries have to date been largely neglected in studies of this kind, yet broadband technology offers potential for a step change in their economic and social development. A growing body of evidence indicates that broadband Internet, and information and communication technologies (ICT) in general, promote economic development. Given its potential applications in diverse sectors of the economy, investment in this technology is particularly important for vulnerable countries. Failure to ensure high levels of broadband access and use may have significant implications for these countries, with the risk of seeing them fall further behind.