Quick definition An ATS is a trading platform operated by a private company. ATSs operate under lighter regulation than exchanges and include both lit venues (with public price quotes) and dark pools (anonymous order matching). What it is ATSs are platforms that match buy and sell orders. Unlike exchanges, ATSs are not exchanges themselves; they are private venues that match buyers and sellers. Nasdaq and NYSE are exchanges. Arca, Island, and Instinet are ATSs. ATSs are regulated but with fewer requirements than exchanges. They do not require companies to meet listing standards; any security that trades on an exchange can also trade on an ATS. Why it matters ATSs provide competition for exchanges. They often offer lower fees, faster execution, or special features that attract traders. ATSs also provide venues for trades that do not fit the exchange model, such as block trades or dark trading. The rise of ATSs has fragmented equity markets, creating complexity for traders who must route orders to multiple venues to achieve best execution. Lit ATS versus dark pools A lit ATS publishes all quotes and trades, similar to an exchange. A dark pool is an ATS that does not publish quotes; it matches orders anonymously. Traders use dark pools to execute large orders without revealing their intent. Practical example You are a trader at a large asset manager. You want to buy 100,000 shares of a company without tipping off the market about your position. You route the order to a dark pool, which matches you with a seller without revealing your demand. The trade executes at the midpoint between the best bid and ask on lit venues. If you had sent the order to a lit venue, the market would see your demand and the price would move against you. Regulation ATSs are registered with the SEC but operate under SEC Rule 15c2-11, which is lighter regulation than the exchange ruleset. ATSs do not have listing standards and do not conduct market surveillance as extensively as exchanges. See also - Venue - Exchange - Dark Pool - Market Fragmentation
