Two features of a new horizontal conceptualization of expertise are explored. Polycontextuality refers to the multiple ongoing tasks apparent in expert work, and boundary crossing is considered as a cognitive process that characterizes much expertise. Three case studies, one in a Finnish elementary school, illustrate these concepts. (SLD)

The four studies presented show how expertise, from the cultural-historical theory of activity, is constructed interactively in everyday problem situations. They also demonstrate that purely situational analyses of discourse are insufficient as attempts to explain expertise. The four studies are presented as individual chapters: (1) Expertise as…