This chapter relates the story of the development of recent ideas relating to ecosystems that are greatly modified by environmental and biological changes. Originally such ecosystems were given attention simply because they were an understudied set of systems that could teach us about how ecological communities assemble and reassemble. However, as the widespread prevalence of such “novel ecosystems” became obvious, some data suggested they could deliver important ecosystem functions. This led to a debate regarding the values, management, and restoration of altered ecosystems. The original papers had a hard time in the review process, and debate has, at times, been rancorous. However, many practitioners and ecologists now find the concept of novel ecosystems useful, and the possibility of their conservation value worth investigating.