I have written a "think piece" published in the December 2009 issue of ASM’s journal, Microbe, in which I list my choices of what constitute paradigm shifts in modern microbiology. The choice was entirely idiosyncratic. I am sure that others would include different important developments on their roster. I also make the point that some apparent P.S.’s are really "paradigm drifts". Chacun à son goût, if you pardon my French. So, here's your chance to expound you views on this matter. What breakthroughs in microbiology do you consider worthy of being called paradigm shifts?