Müller, RalfSankaran, ShankarDrouin, NathalieVaagaasar, Anne-LiveBekker, M.C. (Michiel Christiaan)Jain, Karuna2018-09-032018-01Muller, R. Sankaran, S., Drouin, N. et al. 2018, 'A theory framework for balancing vertical and horizontal leadership in projects', International Journal of Project Management, vol. 36, no. 1, pp. 83-94.0263-7863 (print)1873-4634 (online)10.1016/j.ijproman.2017.07.003http://hdl.handle.net/2263/66431This paper develops a framework for understanding the interaction between person-centered leadership by project managers (a.k.a. vertical leadership (VLS)) and team-centered leadership by individuals in the project team (a.k.a. horizontal leadership (HSL)). It builds on Archer's Realist Social Theory and its morphogenetic cycle, which describes the interaction of structure with agency for task fulfillment and the resulting reshaping (morphogenesis) or continuation (morphostasis) of structure for subsequent iterations of the cycle. Data were collected globally in 33 case studies with 166 interviews and analyzed using Alvesson's Constructing Mystery technique. A theory about the cycles and events that shape the interaction between VLS and HLS is developed, which includes events such as nomination, identification, selection, execution and governance, as well as transitioning. Managerial and theoretical implications are discussed.en© 2017 Elsevier Ltd, APM and IPMA. All rights reserved. Notice : this is the author’s version of a work that was accepted for publication in International Journal of Project Management. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. A definitive version was subsequently published in International Journal of Project Management, vol. 36, no. 1, pp. 83-94, 2018. doi : 10.1016/j.ijproman.2017.07.003.Vertical leadership (VLS)Horizontal leadership (HSL)Shared leadershipBalanced leadershipMorphogenetic cycleProject management (PM)TeamMattersKnowledgeGovernanceTemporary organizationPostprint Article