This book asks why 20th century American Catholics stopped building churches that looked back to the middles ages, and began building churches that for the present and the future. It argues that belief in an evolutionary universe, a biological paradigm, united Catholic liturgists and modernist architects, enabling the development of a futurist architecture. The book explores the use of architectural models and theologians' and architects' interest in the latest technological developments. It traces the influence of theologians like Pierre Teilhard de Chardin, SJ, and Harvey Cox on American Catholics' ideas about worship space. Finally, it examines post-Vatican II renovations and experimentation with the location and arrangement of worship space in the late 1960s and early 1970s. Combining social, cultural, intellectual, and architectural history, the book weaves a story about how American Catholics in a dramatically changing world explored the future of their Church through their ideas about the future of the church building.