This Knowledge Note summarizes the experiences of, and lessons learned by Japanese cities that have designed and implemented various types of urban flood risk management investments. Building on the broad principles outlined in Knowledge Note 2 of the same series, and on a review of 20 cases (detailed in an appendix) across Japan, this note focuses on five categories of investment criteria: flood management and investment objectives, technical considerations, urban development and finance, governance and stakeholders, and multipurpose infrastructure. The specificities of each context inform and determine the enabling environment for investment, and the feasibility and relevance of various mechanisms to manage flood risks. Investing in efforts to reduce and manage urban flood risks requires cities to carefully select those measures that promise to be most effective and efficient in a given context. Cities must be able to understand and weigh the strengths and weaknesses of various options, assess the range of flood management measures available, and consider the enablers needed for implementation. This can be a daunting task, given obvious limits to the information, time, and resources needed to thoroughly understand and explore the array of flood risk management options. This note highlights the following key lessons learned from Japan’s experience in designing and implementing effective flood management investments in urban settings.