Shared understanding is imperative for effective business/IT collaboration. In the past, research has frequently employed a situational snapshot approach, focusing on the degree of business-IT shared understanding at specific points in time. To understand the evolution of shared understanding over time, we conducted a study of four distinct IT projects within a global IT service provider firm. A longitudinal cross-case analysis is employed to identify patterns in the development of shared understanding over time and to uncover explanations for these patterns. We identify common challenges, such as team member involvement or technical details, at various phases of IT projects and provide recommendations on the timing and design of critical actions to overcome these challenges and facilitate a shared understanding. By doing so, we develop propositions on the development of shared understanding and lay the foundation for a process theory of business/IT shared understanding in IT projects.