The articles presented in this special issue focus on a cultural-historical approach to the study of mind, culture, and activity—that is to view individual human development as the emergent outcome of phylogeny, cultural history, and microgenesis. A combination of data is presented, some which is cultural-historical in nature and some from the analysis of the real-time behavior of people of different ages and experiences. Geoffrey Saxe and Indigo Esmonde offer a welcome addition to the small corpus of longitudinal studies in the role of cultural-historical change on cognitive development. They focus on the way in which a particular numerical term changes as a function of historical shifts in local practices of enumeration. Commentaries by Giyoo Hatano and Anna Sfard highlight a variety of important questions concerning both the particular case presented by Saxe and Esmonde and the methodological challenges that such work poses.
