What do market makers do?

Market makers are firms or individuals who continuously quote both bid (buy) and ask (sell) prices for a security, standing ready to transact at those prices. Their primary economic function is to provide liquidity, ensuring that investors can buy or sell without waiting for a matching counterparty. Market makers profit from the bid-ask spread and, increasingly, from sophisticated quantitative strategies that manage inventory risk.

In modern equity markets, the largest market makers (Citadel Securities, Virtu Financial, Jane Street) handle enormous volumes across stocks, ETFs, and options. They receive order flow from brokerages (often through payment for order flow arrangements), internalize trades when profitable, and route to exchanges when necessary. In options markets, market makers are the primary sellers of options to directional traders, creating the gamma exposure dynamics that influence equity volatility regimes.

Market makers take on substantial risk. Holding inventory means exposure to adverse price moves, and the compensation for bearing this risk is embedded in the bid-ask spread. During periods of market stress, spreads widen as market makers demand more compensation for the increased risk of being adversely selected (trading against someone with better information). In extreme cases, market makers may reduce or withdraw liquidity entirely, as occurred during the 2010 Flash Crash.

The evolution of electronic market making has dramatically reduced bid-ask spreads and improved execution quality for retail investors over the past two decades. However, it has also concentrated liquidity provision in a small number of highly capitalized, technologically advanced firms. Understanding market maker behavior is essential for institutional investors because dealer hedging flows, inventory accumulation, and positioning can create predictable short-term price patterns that systematic strategies seek to exploit.