In 1927, Georges Lemaitre argued that our universe is expanding, a conclusion rendered more startling by the astronomical data that backed it up, presented two years later by Edwin Hubble. The speed of this expansion is governed by Hubble's constant, and Discordance tells its troubled history. This unpredictable and fascinating story begins with the first tentative steps to measure the distances to nearby stars and galaxies. It traces the extraordinary interplay between cosmological theory and astronomical observation which has given us the standard Big Bang theory. It was not all plain sailing, and the narrative takes us through the discovery of dark matter, the Hubble Wars of the 1970s, the invention of cosmic inflation, and other crucial scientific moments. Further satellite missions were expected to add to the clarity of our measurements. But from about 2009 onward, the results began to diverge. This is the Hubble tension and perhaps even a crisis. Jim Baggott clearly and entertainingly guides the reader through this gripping scientific voyage one littered with crises of confidence, astonishing discoveries, and extraordinary personalities which still continues today.