Book excerpt: What is a threshold space? A prelude, an intermediate space, a barrier? Inside or outside? The threshold space is all of these, usually even at the same time. He lives on the spatial ambivalence between opening and closing and at the same time creates the expectation of what is to come. Till Boettger has dealt in teaching and research projects closely with the architectural staging of arrival and reception. His book is a collection of exemplary phenomenological analyzes of spatial transitions in historical and modern cultural buildings by renowned architects. It also develops a methodology to optimize threshold rooms in all construction projects. In addition to a balance that can generate an exciting space, there is also primarily the temporal sequence of experiencing determining. Threshold spaces are shown here in their role as a spatial agent: they receive and bid farewell.