CIAM’s exhibitions are a mystery. Despite their prominence within the collection of congresses, meetings, publications and events, they have been overlooked in scholarship. The following article is based on doctoral research at the Technical University of Munich (TUM), which aims to unfold the significance of CIAM’s exhibitions as a working method for and of the Congrès internationaux d'architecture moderne. The research aims to introduce an alternative approach to reframe the canonical histories of CIAM’s congresses and well-known actors. It contributes to the quest for a more complex view on the historiography of architectural modernism. The article puts CIAM’s second exhibition “Rational Lot Development,” first shown at the third CIAM meeting in Brussels in 1930, into the focus. Based on archival material from the CIAM Archives in the gta Archives at ETH Zurich, it deciphers the significance of the exhibition “Rational Lot Development” as space and program for the third CIAM meeting.