Exchange Traded Funds (ETFs) are gaining popularity as passive, low-cost, high-performance investment vehicles. While being traded on the secondary market delivers accessibility to investors, you lose transparency on who owns your products. Data providers supply some clues, but challenges arise when you combine multiple sources to gain visibility. In this article, we unpack ETF data—highlighting the benefits and complexities of each source—and recommend three strategies based on where you are in the ETF market. The most effective strategy will right-size the number of sources balanced against the cost of combining them.