Why is there so much side-by-side management in the ETF industry?

We document the dramatic rise of side-by-side management (“SbS”) in the global ETF industry. As of 2018, around 60% of individual ETF fund managers manage mutual funds in a SbS arrangement, most of which are “active” mutual funds. We argue that mutual fund firms employ SbS arrangements to exploit institutional client relationships of their mutual fund managers to help channel mutual fund TNA at risk of withdrawal to the firms’ new ETF business. Mutual fund managers are most likely to become SbS ETF managers if they generate revenue from institutional TNA and face strong ETF competition. SbS initiations lead to discretionary institutional (but not retail) outflows from mutual funds and contemporaneous inflows in the ETFs overseen by those same SbS managers. Client level holdings tests link these flows to those institutional clients with likely stronger relationship to the SbS managers, suggesting that SbS arrangements are an important tool for traditional mutual fund firms to meet and manage the rise of ETFs.