Trust is a key dimension in business relationships and has been much studied. But less attention has been given to understanding the dynamics and evolution of trust and the causal mechanisms and processes driving this. We propose a process model of the dynamics and evolution of trust in business relations based on a view of business relations as complex adaptive systems. Trust changes depending on the experience and outcomes of the actions and interactions and other events taking place over time in the focal as well as in connected relations. The psychological, social and economic mechanisms driving these changes in trust are identified. Our model has important implications for generating, sustaining and protecting trust in business relationships and networks and for future research.