By Maurice Nussenbaum, published in the volume *Mélanges en l’honneur de Jean-Jacques Daigre* – November 2017
High-frequency trading (HFT) is a product of technological progress. It improves market liquidity by reducing transaction times, but can also lead to abuses. We shall first examine how it works and its effects, then look at the current regulatory framework, before analysing the recent sanctions imposed by the regulatory authorities.