This thesis discusses military operations planning and methodology by reviewing two of NATO’s planning documents, i.e. the ‘Allied Joint Doctrine for Operational-Level Planning’ (AJP 5) and the ‘Comprehensive Operations Planning Directive’ (COPD), and defends the following claim. Parts of the description of NATO’s Operational-Level Planning Process (OLPP), as described in the AJP 5 and the COPD, is methodologically inconsistent (contradictory), due to epistemic and practical implications of methodology. As such, the thesis discusses three topics: approaches to Operational Art, planning heuristics and implications of methodology. The thesis also intertwines military operations planning, methodology and military problem-solving. This thesis consists of two published papers and an introduction. The introduction explains and further discusses operations planning as well as terms and concepts stated within the two papers. Paper I focuses on the AJP 5 and discusses the methodological distinction between two approaches within Operational Art, denoted the ‘Design’ and the ‘Systemic’ approach. The distinction between these approaches is vague and paper I states one epistemic and one practical implication of methodology. Paper II focuses on the COPD and discusses two specific planning heuristics. The first relates to the Systemic approach and the second heuristic relates to the third approach denoted the ‘Causalist’ approach within Operational Art. A methodological contradiction exists between these specific heuristics and paper II states one epistemic and three practical implications of methodology. Briefly, this thesis implies that parts of NATO’s description of the OLPP suffers from a methodological contradiction. Hence, a suggestion is to revise parts of the AJP 5 and the COPD. The thesis also suggest the development of a “NATO handbook of methodology” to better explain methodological implications on military operations planning and the “how to” of military problem-solving. / <p>QC 20170403</p>