The world is currently facing a variety of urban challenges due to rapid economic growth and urbanization, which are expected to intensify further. In particular, the rapid urbanization of developing and underdeveloped countries causes severe hardships for citizens due to inadequate infrastructure, housing shortages, water scarcity, air and waste pollution, traffic congestion, and increased crime. Recognizing these issues as global community challenges, many developed countries and cities are engaging in various international cooperation efforts, such as development cooperation projects(ODA) and public diplomacy. Seoul is one of the few cities in the world that has overcome urban challenges during its rapid post-war development and urbanization, gaining extensive experience and knowledge in the process. As such, Seoul is uniquely equipped to provide practical solutions to urbanization challenges in developing and underdeveloped countries. By promoting ODA projects, Seoul can enhance its international reputation as a responsible global city, strengthen its global influence, and increase its competitiveness on the world stage. To achieve this, Seoul needs to actively pursue ODA projects that empower urban (local) governments to address urban challenges independently. This involves identifying cooperation areas that overseas cities require and exploring various practical solutions. Particularly, Seoul must establish selection criteria and grouping mechanisms for partner cities to ensure systematic implementation of ODA projects. For systematic ODA promotion, many governments and developed countries establish both quantitative and qualitative selection criteria for their cooperation targets. However, while some countries disclose general principles for selection, few provide detailed criteria for identifying priority countries, often to avoid international controversies or conflicts. Most countries, including Korea, combine quantitative indicators and qualitative elements to select cooperation targets(priority partner countries). No country relies solely on quantitative indicators; instead, they consider factors such as the feasibility and potential success of cooperation, alignment with international standards, national strategies, and foreign relations. Accordingly, Seoul should also develop selection criteria for partner cities, considering factors such as the necessity and feasibility of cooperation, expected outcomes, diplomatic relations, policy directions, visions, and international standards. Initially, Seoul could identify and group cities based on existing relationships, such as friendly sister cities or prior cooperation experience. These cities should also align with international standards, such as being capital or secondary cities in Korea's priority ODA partner countries or being included in the OECD DAC list of aid recipient countries. The grouped cities can then be prioritized based on cooperation effectiveness, necessity, and strategic alignment. Quantitative criteria should include internationally recognized data such as the Human Development Index(HDI), Democracy Index, GDP per capita, GNI per capita, and urbanization rates. Qualitative criteria could include the feasibility and willingness of the target city to implement projects, sustainability of initiatives, and alignment with Seoul's global "Companion for the Vulnerable" policy. Unlike the central government, Seoul faces budgetary and manpower constraints, requiring a focused approach to ODA to achieve tangible results. To this end, Seoul needs to identify areas and projects desired by overseas cities and concentrate efforts accordingly. Developing modularized documentation of Seoul's successful policies, accessible for partner cities and institutions, would greatly facilitate this effort. Seoul’s "Policy Archive," which currently contains 375 entries, serves as a foundation. However, despite the existence of numerous successful policies and projects since the start of modularization efforts in 2014, there has been limited expansion into new fields and projects. Seoul must reflect on its evolving policies, administrative systems, and changing urban environments to create new policy modules tailored for international cities and institutions. The content of Seoul’s policy modularization and its ODA strategies for grouped cities should be designed based on the developmental needs of the target cities and the international community. Unlike the existing one-size-fits-all format, the modularization should consider the nature of policies and projects and classify them into six types for practical use by overseas cities: Module Paper, Overview Paper, Sector Paper, Issue Paper, Case Manuscript, Advice Paper. Seoul's ODA strategy for grouped cities should focus on the development areas with the highest demand, organizing smaller groups accordingly. Analyzing 100 partner cities reveals that urban challenges such as transportation, infrastructure, environment, and housing are particularly severe. Hence, the strategy should prioritize the following Subgroup 1-1 Focus on transportation and infrastructure. Subgroup 1-2 Address environmental and transportation issues. Subgroup 2-1 Prioritize environmental challenges. Subgroup 2-2 Focus on transportation and environmental issues. Subgroup 3-1 Address transportation, infrastructure, and environmental issues. Subgroup 3-2 Focus on transportation, infrastructure, and housing development.