At the end of 2018, London's biggest engineering project came to fruition. For the first time, trains run through the tunnels built under central London between Paddington and Liverpool Street. Driving through a subterranean world of rock and mud; employing digital technology at the extreme cutting edge; and realizing a vision of east-west metropolitan access conceived in the era of Attlee and Churchill--Crossrail is an engineering marvel of the 21st century. Here Christian Wolmar tells its amazing story. Engaging with both historical and social perspectives, he outlines the postwar history of the idea of a trans-London east-west railway line, the proposals of the 1970s, 1980s, and 1990s, the passing of the Crossrail Act of 2008, and the lengthy and complex engineering processes that brought the new line into being.