There has been and still is a lot of controversy on whether pair programming is a useful engineering technique - as if this would not strongly depend on the specific goals, task, and the pair's pair programming skill. Rather than providing still more bottom-line, quantitative results on pair programming, a research group at Freie Universität Berlin set out to decipher what is the actual process of pair programming and what is pair programming skill. This book contains a set of concepts that serves as the infrastructure for studies of pair programming that focus on qualitative data analysis. It promises to connect the results of such studies to one another. The book is oriented towards researchers only, not towards practitioners.