Recent publications reveal that high frequency trading (HFT) is responsible for 10 to 70 per cent of the order volume in stock and derivatives trading (Gomber et al. 2011; Hendershott and Riordan 2011; Zhang 2010). This observation leads to a controversial debate over positive and negative implications of HFT for the liquidity and efficiency of electronic securities markets and over the costs and benefits of and needs for market regulation. Currently the European Union (EU) is considering the introduction of a financial transaction tax to curtail the harmful effects of HFT strategies. The consideration behind this market policy is based on the assumption that the very short-term oriented HFT trading strategies lead to market frictions. This current discourse shows that the arguing parties do not homogeneously define HFT. Reasons for this are the proponents’ different but intertwined perspectives, which lead to new unanswered questions in numerous subjects of expertise.