There is growing international concern about the threat to public health of the emergence and spread of bacteria resistant to existing antibiotics. An effective response must invest in both the development of new drugs and measures to slow the emergence of resistance. This paper addresses the former. It focuses on low and middle-income countries with pluralistic health systems, where people obtain much of their antibiotics in unorganised markets. There is evidence that these markets have enabled people to treat many infections and reduce mortality. However, they also encourage overuse of antibiotics and behaviour likely to encourage the emergence of resistance. The paper reviews a number of strategies for improving the use of antibiotics. It concludes that effective strategies need measures to ensure easy access to antibiotics, as well as those aimed at influencing providers and users of these drugs to use them appropriately.