Metabolism, the Japanese architectural avant-garde movement of the 1960s, profoundly influenced contemporary architecture and urbanism. This book investigates the Metabolists' utopian projects of the city, which often envisioned the sea and the sky as human habitats of the future and proposed three-dimensional urban forms on an unprecedented scale - often known as megastructure. This comprehensive account focuses on the movement's urbanism and utopianism, situating it in the context of Japan's mass urban reconstruction, economic miracle, and socio-political reorientation.