JA110 is a special issue devoted to building sites. Building sites are places where buildings spring up—where architectural ideas assume physical forms. In this issue, we used building sites as points of departure to examine the processes of trial and error in which architects engage to realize their buildings.When Japanese architects are on building sites, what do they look at? How do they investigate and make decisions? There is a trend for them to be actively involved in on-site developments and to include construction processes in the scope of their designs. Whereas the inner workings of a building is usually hidden once a buildings is completed, they are visible on site, while construction is underway. If one pays close attention to what transpires on the site, one may observe the moment when an architect's ideas and consciousness about making things are sublimated into the building and its spaces.This issue includes site photos and comments from 17 recent buildings as well as buildings completed during the 1950s through 1980s. We hope these building sites, both new and old, will serve as opportunities to explore relationships between the architects's thinking and the physical things they create.