I will provide a brief introduction to HFT (High Frequency Trading) and some definitions. I will then elaborate on 2 major effects of HFT on the markets. First is the effect on price structure and how it changes. I will then touch on the underlying "war" between classes and families of algorithms (not only HFT). I will conclude with the effects of HFT on methods that attempt to frame price structure and show a real market example - during planned news - and what can happen in those cases.