Exchange traded funds (ETFs) that track a specified index are a financial technology that has risen dramatically in the last two decades. We model an ETF's optimal index replication strategy and show that it involves underweighting or omitting illiquid index assets. Instrumenting for ETF trading...

This paper examines how the rise of passive investing affects active management. I develop a parsimonious model of passive and active investment in which greater passive investment accelerates investors' learning about active managers' skill. The model provides a rational explanation, namely the...