The markets and competition policy assessment toolkit (MCPAT) is a guide for understanding how policy can positively shape markets and address market failures that ultimately affect micro- and macroeconomic development issues. The MCPAT aims to support policymakers, competition authorities, and development finance institutions in realizing the advantages of competitive and well-functioning markets by setting the right conditions for firms to improve their economic performance and for markets to allocate resources efficiently. Competitive and well-functioning markets do not just benefit consumers, - they benefit entire economies as they promote productivity, innovation, efficiency, and consumer choice. The goal is not simply to increase the number of firms in a market or to restrict market power but to create an environment where competition can thrive, firms can innovate, and markets can function optimally. The structure of this toolkit follows the steps to conduct an MCPAT analysis in a specific sector or market. Part I provides an overview of key concepts that set the basis for conducting the MCPAT analysis and covers the first step of the MCPAT. Part II focuses on diagnosing market issues. Part III is about how to fix markets.