Scholars and practitioners have widely advocated the use of green infrastructure for water quality improvements. The United States has witnessed an emphasis on cost-effectiveness and co-benefits as the federal government has enforced green infrastructure planning in some Clean Water Act compliance cases. In addition, planning scholarship generally assumes that a growing number of cities are adopting green infrastructure. How and to what extent cities have integrated green infrastructure into institutional planning, however, is a subject that has received little attention. This dissertation evaluates the status of institutional green infrastructure planning and investigates the impact of federal mandates on the institutionalization. This research consists of two phases: a landscape study to understand the overall status of green infrastructure planning to control stormwater and combined sewer overflows, and an in-depth study to highlight how each federal mandate impacted differences. Phase 1 first characterizes green infrastructure elements in U.S. Environmental Protection Agency consent decrees and the planning documents of 41 local governments. Based on the content analysis findings, I then examined the impact of federal mandates on planning and implementation status. Phase 2 takes a comparative analysis of two cases: the maximum and minimum federal direction cases. I conducted semi-structured interviews to add nuance in actual practice and used Google Street Views to exhibit the differences in mandated projects and changes in pre- and post-construction conditions. The results of the landscape study demonstrate a lack of standardization in federal enforcement as well as local green infrastructure planning to control stormwater and combined sewer overflows. The case studies suggest that green infrastructure may not be a cost-effective and multifunctional solution for sewer authorities, especially in terms of CSO reduction. The findings also indicate room for both regulatory and planning improvements to better institutionalize green infrastructure planning while facilitating desired outcomes. The dissertation concludes with policy and planning recommendations for regulatory bodies and local governments, including a measurable goal setting through a phased approach, an evaluation framework with more frequent performance reviews, a robust and strategic pilot project plan, a community- and project-specific co-benefit analysis, and a cost-sharing scheme.