This Article provides the first detailed empirical analysis of the landscape of U.S. stock market indices. First, I hand collect detailed information about the universe of indices used as benchmarks for U.S. mutual funds. I document substantial heterogeneity across indices and find that the overwhelming majority of the indices in my sample are used as a primary benchmark by only a single fund. I then turn to “passive” index funds and find that both these phenomena are even more extreme among the indices that these funds track. Far from being “passive,” my findings indicate that index investing is better understood as a form of delegated management, where the delegee is the index creator rather than the fund manager. Finally, I turn to ETFs and find that a substantial fraction of these funds track indices that they or their affiliates create. Even controlling for other factors, I find that these funds have, on average, higher expense ratios. My findings shed light on an overlooked part of the financial market and have substantial implications for investor protection.