This article analyses comparative data from the 1994-1998 International Adult Literacy Survey (IALS) and the 2012 Programme for the International Assessment of Adult Competencies (PIAAC). At the micro level, the author considers factors involved in the development of an individual person's literacy from a lifecycle perspective. At the macro level, he investigates trends in literacy proficiency profiles for countries that participated in both the IALS and PIAAC studies. In a number of countries, small average declines in literacy were recorded. This apparent stagnation in overall literacy at the population level in so many member countries of the Organisation for Economic Cooperation and Development (OECD) merits a closer look at the trend data made available from IALS and PIAAC. The aim of this research is to understand the determinants of literacy proficiency in terms of (1) how they may be affecting the development of literacy from an individual lifecycle perspective, and (2) how they may be affecting the development of national profiles of literacy proficiency as countries' sociodemographic compositions, sociocultural practices and economies change over time. There are few other comparative data like these that can help to improve insights on what drives the development and maintenance of literacy in adult populations. The data suggest that macro trends in literacy practices in work-related contexts may be on the decline, an impression the author discusses in relation to the observed stagnation in literacy profiles across many of the countries for which trend data are available. He considers the implications of his findings in relation to the upskilling and deskilling of occupations, changes in the distribution of work tasks, and the continued measurement of practices in PIAAC.