In this article, we present a perspective on the interaction between formal and informal institutions in spatial planning in which they transform each other continuously, in processes that can be described and analyzed as ongoing reinterpretations. The effects of configurations and dialectics are often ambiguous, only partially observable, different in different domains and at different times. By means of analyses of key concepts in planning theory and practice, this perspective is illustrated and developed. Finally, we analyze transformation options in planning systems, emphasizing the limits of formal institutions in transforming formal/informal configurations, and stressing the importance of judgment and conflict.