The ad hoc formation of interorganizational relationships and networks remains a black box for management scholars. We address this phenomenon by investigating interorganizational responses to an extreme event. Hence, we explore how interorganizational constellations of previously unconnected actors formed in response to the large-scale outbreak of enterohemorrhagic Escherichia coli (EHEC) in Germany in 2011, which killed 53 people and affected over 4,000. We present a preliminary model of interorganizational assemblage and offer propositions that highlight the conditions under which the development of collaborations across organizations is made possible in face of crises.