Transportation as we know it is changing profoundly: people are driving less, “walkability” is driving real estate and economic development, transportation apps and the sharing economy are changing our driving habits, and the self-driving car is on the horizon. What do these changes mean for our cities? On what terms shall we incorporate technological change into our built environment and into our lives? The city of the 20th century became the city of the automobile. Today, amid accelerating change, we are presented with new choices. What shall the city of the 21st century be?