This article reports an investigation into project managers' perceptions of managerial complexity. Based on a multistage empirical study, elements of “what makes a project complex to manage” were identified and classified under the dimensions of mission, organization, delivery, stakeholder, or team—the MODeST model. Further, the data showed that these elements had both structural and dynamic qualities and that the elements are interdependent. Project managers are shown to be embedded in this complexity. The practical implications of the research include the ability to describe managerial complexity in a manner consistent with the actuality of the lived project environment. This provides a framework for the description of the level of managerial challenge or difficulty, which will allow the assessment of individual and organizational responses to it in the future. Further, the opportunity exists for active management of complexity.