We investigate the determinants of CIOs' organizational role and tasks. We first review previous studies, which we classify as either evolutionary or CIO role studies. We consider them to be characteristic to the usage of certain technologies or certain periods of times. We modify Leavitt's well-known model to describe factors that shape the role and the tasks of CIOs over time, industries and technologies. We validate the model from interviews with 36 CIOs within six industries covering the time period from 1960s to present times. We also show that the model can be used to categorize prior research findings. We then use the model to describe how business strategy impacts CIOs' role and tasks and how changes in business strategy influence CIOs and vice versa. We discovered that the modified Leavitt model is a useful description of factors that both define CIOs' role and tasks at any particular time in any specific organization, and show how those tasks change.