Chemical manipulation is a central tool for biology, complementing genetic engineering. However, it is important that these chemical tools have to be safeguarded for undesired side effects, so called artifacts (ars = art, factum = made) that lead to false interpretations. The use of appropriate controls is essential. To design these controls and to interpret the effects of inhibitors correctly, it is vital to know the mode of action of the respective inhibitor. On these pages, we will compile the necessary information to use inhibitors correctly.