For centuries, many European cities and towns managed to accommodate growth and change while sustaining the historic character that, in modern times, has brought them recognition as cultural resources of high artistic value. All living organisms, too, must negotiate the competing claims of constancy and change through processes of adaptation that have long been the subject of scientific investigation. Recent developments in urban theory advocate the conscious application of similarly adaptive strategies for maintaining balance between necessary change and the conservation of historic character in the built environment. Rome, with its millennia of construction, alteration, demolition, and rebuilding, offers the clearest example of how different kinds of change—both adaptive and catastrophic—impact the city over time. After a half-century or more of architecture and urbanism that departed from traditional practice and privileged contrast with preexisting conditions over formal continuity, historic centers have come under a new threat. The idea of adaptation offers an alternative that redefines urban conservation practices in the interest of sustaining historic character over the long term, while permitting necessary growth and change.