The Financial Information eXchange (FIX) protocol is an electronic communications protocol initiated in 1992 for international real-time exchange of information related to securities transactions and markets. With trillions of dollars traded annually on the NASDAQ alone, financial service entities are employing direct market access (DMA) to increase their speed to financial markets. Managing the delivery of trading applications and keeping latency low increasingly requires an understanding of the FIX protocol.

The FIX protocol specification was originally authored in 1992 by Robert "Bob" Lamoureux and Chris Morstatt to enable electronic communication of equity trading data between Fidelity Investments and Salomon Brothers. FIX initially addressed information between broker-dealers and their institutional clients. At the time, this information was communicated verbally over the telephone. Fidelity realized that information from their broker-dealers could be routed to the wrong trader, or simply lost when the parties hung up their phones.

It wanted such communications to be replaced with machine-readable data which could then be shared among traders, analyzed, acted on and stored. For example, broker-dealers call with an indication of interest (IOI) to buy or sell a block of stock. The FIX initiative created new messages such as the IOI.

According to the FIX Trading Community, FIX has become the de facto messaging standard for pre-trade and trade communication in the global equity markets, and is expanding into the post-trade space to support straight-through processing, as well as continuing to expand into foreign exchange, fixed income and derivatives markets.

The FIX Trading Community is a non-profit, industry-driven standards body with a mission to address the business and regulatory issues impacting multi-asset trading across the global financial markets through the increased use of standards, including the FIX Protocol messaging language, delivering operational efficiency, increased transparency, and reduced costs and risk for all market participants.

FIX is widely used by both the buy side (institutions) as well as the sell side (brokers/dealers) of the financial markets. Among its users are mutual funds, investment banks, brokers, stock exchanges and ECNs.

FIX has become the standard electronic protocol for pre-trade communications and trade execution. Although it is mainly used for equity transactions in the front office area, bond derivatives and FX-transactions are also possible. One could say that whereas SWIFT is the standard for back office messaging, FIX is the standard for front office messaging. However, today, the membership of FIX Protocol Ltd. is extending FIX into block trade allocation and other phases of the trading process, in every market, for virtually every asset class.

Originally, the FIX standard was monolithic, including application layer semantics, message encoding, and session layer in a single technical specification. It remained monolithic through FIX version 4.2. Thereafter, message encodings and session layer specifications began to be split into separate documents, and ultimately, FIX evolved into a family of related technical standards.