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Citadel Securities is a market maker that buys and sells stocks and options on behalf of retail and institutional investors, earning money on the tiny gap between what buyers pay and sellers receive.
Citadel Securities is one of the biggest market makers in the world. When you tap "buy" on a stock or option in a trading app, there's a good chance Citadel Securities is on the other side of that trade, quietly buying from you or selling to you in a fraction of a second. It doesn't run a flashy consumer brand; it works in the background, keeping markets moving.
Here's the basic problem it solves. Markets need someone willing to trade at any moment, even when no obvious buyer or seller is around. That's the market maker's job. Citadel Securities constantly quotes prices at which it will buy and sell, and it profits from the small spread between those two prices — like a currency exchange booth that buys your dollars a little cheaper than it sells them. Multiply tiny spreads across billions of shares and options a day, and it adds up to a huge business. Its main customers are retail brokers, who route their users' orders to firms like Citadel Securities for execution, plus banks and institutional investors who need to trade large blocks quickly. The rise of commission-free retail trading supercharged this model. When apps like Robinhood made trading free, the brokers began earning money by selling their order flow to market makers instead of charging customers. Citadel Securities became the largest destination for that retail order flow, and it now handles a staggering share of U.S. retail stock trades. That dominance has made it a lightning rod: critics argue the setup can create conflicts of interest and disadvantage ordinary investors, while the firm says it delivers better prices and tighter spreads than public exchanges. Regulators have repeatedly examined the practice, and the debate over payment for order flow is one of the most closely watched issues in U.S. market structure.
Citadel Securities is a private company, separate from the hedge fund Citadel-linked asset manager of the same broader name, though both trace back to founder Ken Griffin. It's a powerhouse precisely because speed and scale matter enormously in market making — the faster and more reliably you can quote prices, the more volume you attract, and the more money you make on those razor-thin spreads. Its biggest vulnerabilities are regulatory changes to order flow rules, competition from other big market makers, and the simple fact that its fortunes rise and fall with how much ordinary people and institutions trade.
Saved answer · last researched 15 Nov 2026