<p>Team psychological safety is widely recognized as a critical ingredient in high-performing teams. However, little is known about how team psychological safety emerges and develops over time. Drawing on the input-process-state-output (IPSO) team dynamics framework, we conducted two multiple case studies across different contexts to explore the temporal dynamics of team psychological safety in short- and long-term project teams. Our findings suggest that team psychological safety is a perishable resource that can diminish as well as grow over time. In our studies, these dynamics were shaped by team member interactions, which manifested in four key team processes: <i>connecting, clarifying, supporting,</i> and <i>performing</i>. Importantly, team psychological safety did not arise as a passive consequence of time spent together. Instead, it resulted from how teams actively spent their time and which processes they sustained. We discuss the theoretical and practical implications of these findings and suggest directions for future research.</p>