We summarize what we have learnt about kaon production in nucleus-nucleus collisions over the previous decade. We will address three questions. (a) Is the K⁺ production sensitive to the nuclear equation of state? (b) How can it happen that at the same excess energy the same number of K⁺ and K^- are produced in heavy-ion collisions although the elementary cross section in pp collisions differs by orders of magnitudes? and (c) Why do kaons not flow?