This thesis investigates the difficulties and challenges experienced in the first strategic planning process of the Turkish Ministry of Interior (MoI) between the years 2007 and 2013 through case study method. Specifically, it documents how and why top-down, mandatory and formal strategic planning in a one-size-fits-all fashion can be poorly implemented through an authoritative and bureaucratic ministry located in the Turkish central government, within the context of a highly centralised and dynamic policymaking environment. Triangulating data from multiple sources, the research applies the theories of rational planning and incrementalism to the case through a pattern-matching approach along with a rival explanation logic in order to explain the structures and mechanisms that lead to ineffective practice in strategic planning in the MoI. The research proposes a variety of underlying mechanisms for ineffective strategic planning that originate from; the formal-legal strategic planning framework, environmental and institutional contingencies, socio-political factors, cultural tendencies, practitioners’ actual practice, culture of democracy, public service and domain characteristics, organisational memory, leadership, values, external powers and tendencies. The research argues that no single theory fully explains the strategic planning process and practice of the MoI, although incrementalism fits better than rational planning. It proposes a rule-based decision-making mental model as a generative mechanism that leads, in interaction with other mechanisms, to incremental analysis. It demonstrates that incremental decision-making may still continue in a public organisational setting while formal strategic planning is in force and legally binding. The research concludes that the application of strategic planning does not produce automatic results, at least in the short-run, and effective strategic planning requires transformation of mental models from rule-based to goal-based, which can be made possible by the effective intellectual preparation of strategy practitioners. Thereby, the research calls for increased attention on strategy practitioners and their actual practice in strategic planning processes.