Exchanges, Market Infrastructure and Trading

Behind every stock trade on a phone sits a chain of businesses that almost nobody sees: the broker that takes the order, the wholesaler or exchange that fills it, the clearing house that guarantees it, the depository that records who owns what, and the data vendors that sell the prices to everyone else. These are some of the best businesses in finance. CME Group reported record 2025 revenue of ~$6.5 billion on a record 28.1 million contracts a day; Intercontinental Exchange reported its 20th consecutive year of record revenue at ~$9.9 billion; Nasdaq passed $5 billion of net revenue, with ~$4 billion from software and data rather than trading (company results, early 2026). Citadel Securities reportedly earned a record ~$12 billion of trading revenue in 2025. Meanwhile retail trading, zero commissions, payment for order flow, prediction markets and near-24-hour trading reshaped the market's front end. This section explains how exchanges, clearing houses, market makers and brokers make money, why the industry drifted from trading fees to data and software, how market structure (Reg NMS, PFOF, T+1, the 2024 tick-size reforms) shapes profits, and what the landmark failures (the flash crash, Knight Capital, the Facebook IPO, GameStop) teach.