Kaon production at subthreshold and threshold energies

We summarize what we have learnt about kaon production in nucleus-nucleus c ollisions 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 p roduced in heavy-ion collisions although the elementary cross section in pp collisions differs by orders of magnitudes? and (c) Why do kaons not flow?