As fundamental and yet open as the concept of space may be for architecture, the definitions and demands that it brings with it are no less complex. Which criteria are at the bottom of a particular space and in what way do they inform its aesthetic, functional and social significance? The spatial concepts associated with Neues Bauen in the 1920s stand in general for clarity, rationalism, functionality, as well as for openness, generosity and, particularly with Mies van der Rohe, the human measure. The 13th krefelder architekturtage is dedicated to Mies van der Rohe’s understanding of space and to modernist architecture in its aesthetic and sociological dimensions. At the same time the conference will adopt a philosophical angle and inquire into the possibilities and prerequisites for describing the content of architectural spaces and passing qualitative judgement on them.