BACKGROUND: Many countries, including Kenya, face challenges in ensuring equitable access to essential medicines. National essential medicines lists (EMLs) are policies to select priority medicines for which access should be ensured. The literature on the influences shaping EML formulation and implementation is scarce. This thesis aims to understand the factors that influence the policy processes of EML selection and implementation in Kenya to identify strategies to improve access to essential medicines. METHODS: Through a case study, I explored Kenya EML (KEML) policy formulation (revision) at national level and implementation at national (macro), subnational (meso) and health facility (micro) levels. I used a qualitative health policy analysis approach, guided by a conceptual framework adapting the policy triangle and multiple governance frameworks. 41 semi-structured purposively selected interviews with key stakeholders were conducted and data were gathered through documents and non-participant observations. Deductive and inductive thematic analysis was applied. RESULTS: Findings on the KEML revision highlighted that the medicine selection process was affected by resource constraints, evidence use limitations, insufficient stakeholder engagement, inadequate institutionalisation of the National Medicines and Therapeutics Committee, and the political context of universal health coverage. Macro- and meso-level factors influencing implementation included inadequate KEML dissemination and communication, insufficient medicines financing, and procurement restrictions. Support and accountability by sub-county health managers for health facility procurement and supply management facilitated implementation. At the micro-level, KEML uptake was constrained as it was perceived primarily as a procurement tool by healthcare workers, reflecting limited KEML awareness and knowledge. Local discretion in selecting KEML medicines was exercised based on perceived KEML content limitations, prescriber preferences, and through hospital medicines and therapeutics committees. Implementers were also often not provided the human or infrastructure resources to meet KEML goals. CONCLUSION: The KEML revision process could particularly benefit from more representative stakeholder engagement and context-relevant evidence to guide decisions. Other strategies include institutionalised medicines and therapeutics committees at national and local levels, functional information channels between national and local levels, and alignment of the KEML with clinical guidelines and health financing policies. This study illustrates medicine selection as a multi-level process shaped by macro-, meso- and micro-level actors and contexts.