Temporary organizations (TOs) are organizational forms characterized by finite-life duration, novel tasks, heterogeneity of organizational members, and different phases of work. They have a greater proportion of emergent processes than more enduring organizations do. This poses particular challenges in the use of IT because it is difficult to foresee all IT applications that are required. This paper examines how IT is used to support the execution of processes in TOs. The empirical setting for our study is a particular and exemplar temporary organization: the 2016 Olympic Games Organizing Committee. Through immersive, in depth and qualitative fieldwork, based on participant observation, interviews, and internal documents, we find that TOs have a dynamic mix of operational processes in different phases of work. Accordingly, they have four patterns of IT use: (1) planned use - of formal IT, (2) planned use - of informal IT, (3) emergent use - of informal IT as a substitute for formal IT, and (4) emergent use - of informal IT combined with formal IT. We develop a theoretical explanation for how the patterns address the distinctive conditions facing TOs (i.e. a novel task done in a finite time, by multiple and heterogeneous people, across different phases of work) and its dynamic mix of processes through both planned and improvised use of IT. Practical implications include the impact of improvised IT use on aspects such as security, compliance, integration, and traceability.