In financial markets, high-frequency trading HFT is a type of algorithmic trading characterized by high speeds, high turnover rates, and high order-to-trade ratios that leverages high-frequency financial data and electronic trading tools. A substantial body of research argues that HFT and electronic trading pose new types of challenges to the financial system. High-frequency trading has taken place at least since the s, mostly in the form of specialists and pit traders buying and selling positions at the physical location of the exchange, with high-speed telegraph service to other exchanges. On September 2, , Italy became the world's first country to introduce a tax specifically targeted at HFT, charging a levy of 0. The high-frequency strategy was first made popular by Renaissance Technologies  who use both HFT and quantitative aspects in their trading. Many high-frequency firms are market makers and provide liquidity to the market which lowers volatility and helps narrow bid-offer spreads , making trading and investing cheaper for other market participants.
The use of computer algorithms in securities trading, or algorithmic trading, has become a central factor in modern financial markets. The desire for cost and time savings within the trading industry spurred buy side as well as sell side institutions to implement algorithmic services along the entire securities trading value chain. This chapter encompasses this algorithmic evolution, highlighting key cornerstones in it development discussing main trading strategies, and summarizing implications for overall securities markets quality. In addition, it touches on the contribution of algorithmic trading to the recent market turmoil, the U. Flash Crash, including the discussions of potential solutions for assuring market reliability and integrity. Keywords: algorithmic trading , high-frequency trading , trading technologies , smart order routing , direct market access. In the past few decades, decades, securities trading has experienced significant changes as more and more stages within the trading process have become automated by incorporating electronic systems.