Literacy is a complex and dynamic phenomenon that varies across time, language, and geography. The origins of literacy can be traced back thousands of years, initially invented as a tool for communication to be shared amongst only a small portion of 'educated' human society. However, within the past few centuries, many societies have experienced transitions from mostly illiterate to predominantly literate populations through a variety of means involving both formal and informal learning. The present review considers literacy in a global perspective, with short sections that review: the history and definition of literacy; life-span perspectives; and finally some challenges and opportunities for the future.