Since the establishment of the International Development Association’s (IDA’s) Private Sector Window (PSW), there have been concerns about its structure, use of blended finance, and the inability to measure its progress and impact. With the start of IDA21 replenishment discussions, it is an appropriate time to analyze the PSW – especially to understand whether and how it is mobilizing the private sector. Finally, in the context of broader MDB reform efforts, how do we scale up private capital mobilization to close the significant financial gaps needed to meet the Sustainable Development Goals?