Kermit the Frog famously said that it isn’t easy being green, and in Living at Micro Scale David Dusenbery shows that it isn’t easy being small—existing at the size of, say, a rotifer, a tiny multicellular animal just at the boundary between the visible and the microscopic. “Imagine,” he writes, “stepping off a curb and waiting a week for your foot to hit the ground.” At that scale, we would be small enough to swim inside the letter O in the word “rotifer.” What are the physical consequences of life at this scale? How do such organisms move, identify prey and predators and (if they’re so inclined) mates, signal to one another, and orient themselves? In clear and engaging prose, Dusenbery uses straightforward physics to demonstrate the constraints on the size, shape, and behavior of tiny organisms. While recounting the historical development of the basic concepts, he unearths a corner of microbiology rich in history, and full of lessons about how science does or does not progress. Marshalling findings from different fields to show why tiny organisms have some of the properties they are found to have, Dusenbery shows a science that doesn’t always move triumphantly forward, and is dependent to a great extent on accident and contingency.