Electronic Communication Network
An electronic communication network (ECN) is a type of alternative trading system that automatically matches buy and sell orders entered by market participants at specified prices, displaying quotes in the public market and providing direct access to the order book for subscribers, typically broker-dealers and institutional investors.
ECNs emerged in the late 1990s as a disruptive force in U.S. equity trading. Before ECNs, the Nasdaq dealer market was dominated by market makers who set wide bid-ask spreads and transacted as principals. ECNs — beginning with Instinet (founded 1969 but gaining prominence in the ECN era) and Archipelago (1996) — allowed institutional investors and broker-dealers to post limit orders that competed directly with market maker quotes, dramatically narrowing spreads and improving price transparency.
The defining characteristics of an ECN relative to other trading systems are that it displays firm quotes in the consolidated market data feed (making it a 'lit' venue in market structure terminology) and provides direct subscriber access to post and interact with the order book via electronic connections. Users of an ECN can see the best bid and offer, submit their own orders at specified prices, and access execution without the intermediation of a traditional market maker.
Most major ECNs that emerged in the late 1990s eventually registered as national securities exchanges. Archipelago merged with the NYSE in 2006. Island ECN was acquired by Instinet, which was subsequently acquired by Nasdaq. BATS Trading registered as an exchange in 2008 and was later acquired by Cboe Global Markets. This migration from ATS to full exchange registration reflected both the commercial advantages of exchange status and the regulatory pressures of operating high-volume lit markets under the lighter ATS framework.
Today, the largest U.S. equity venues operate as registered exchanges rather than ECNs, but the ECN model fundamentally transformed how those exchanges work. Modern exchange matching engines are direct descendants of the ECN architecture — continuous double auctions matching orders by price-time priority, with transparent order book access for subscribers and real-time data distribution to the consolidated tape.
The term ECN remains in use as a descriptor for the model rather than a distinct regulatory category, since most large ECNs have converted to exchange status. For retail investors, the key legacy of the ECN era is the tight spreads and transparent pricing that are now standard in U.S. equity markets, a direct result of the competition that ECNs introduced to a previously dealer-dominated market structure.