Principals can influence instruction by working through the linkages that govern teacher behavior. What these linkages are, how they affect instruction, and the impact of the principal on them are the focus of this paper. Two kinds of linkages are distinguished: bureaucratic and cultural. An explantation of both, with particular attention to cultural linkages, is made. The contribution of the high school principal is complicated by the fact that high schools are more loosely linked than elementary schools. Yet, past research attended extensively to bureaucratic linkages without analyzing cultural linkages. It is argued that the high school principal has access to weak linkages of both kinds. The task for the principal is to employ the full range of linkages consistently through a multitude of major and minor actions, in order to generate a common purpose and effect in the school. (Author/TE)