I'm a former high frequency trader. And following the tradition of G.H. Hardy, I feel the need to make an apology for my former profession. Not an apology in the sense of a request for forgiveness of wrongs performed, but merely an intellectual justification of a field which is often misunderstood.In this blog post, I'll attempt to explain the basics of how high frequency trading works and why traders attempt to improve their latency. In future blog posts, I'll attempt to justify the social value of HFT (under some circumstances), and describe other circumstances under which it is not very useful. Eventually I'll even put forward a policy prescription which I believe could cause HFT to focus primarily on socially valuable activities.