O ne interesting feature of de-extinction-particularly with respect to long-extinct species such as the passenger pigeon, thylacine, and mammoth-is that it does not fit neatly into the primary rationales for adopting novel ecosystem-management and species-conservation technologies and strategies: efficiency and necessity. The efficiency rationale is that the new technology or strategy enables conservation biologists to do what they already do more effectively. Why should researchers embrace novel information technologies? Because they allow scientists to better track, monitor, map, aggregate, and analyze species behaviors, biological systems, and human-environment interactions. This enables better decision-making about how to protect species, which areas to conserve, and how to reduce anthropogenic impacts on ecological systems. Many projects in conservation genomics are justified in this way. They involve doing the sorts of things that conservation biologists already do, but they bring new tools to bear on them. Captive breeding programs of endangered species are common. Analyzing the genomes of the individuals involved to increase genetic diversity and avoid inbreeding-as is being done with the island fox in California and the owl parrot in New Zealand, for example-simply increases the likelihood of positive outcomes.The necessity rationale is that unless the novel technique or technology is adopted, the conservation effort will fail. Why should species threatened by climate change be transferred to locations beyond their historical ranges? Because they will go extinct from anthropogenic climatic and ecological changes if they are not. Many applications of conservation genomics are justified in this way. Why should we embrace the genetic modification of the American chestnut? Because it is the only way to establish resistance to the blight that has decimated them. Why should we sequence and synthesize the genomes of frozen specimens of black-footed ferrets? Because it is the only way to increase the genetic diversity of their population enough for long-term viability.The efficiency and last-resort rationales involve reasoning about means-about what is necessary to achieve a goal or how to achieve a given goal most effectively. Introducing the novel technology or technique does not bring into question or require a rethinking of the aim of the conservation activity. The goal is to preserve at-risk species, and the reasoning offered is that we should be open to adopting these new tools and methods because they are conducive to achieving that end. Therefore, debate about the technology tends to focus on whether they can be employed responsibly and whether there is anything ethically objectionable about pursuing conservation in such ways.Of course, it is also possible to use many of these technologies and methods for other ends. Assisted colonization can be and is being done for aesthetic and economic reasons as well as for conservation purposes. The same is true of genetic modification, synthetic genomics, and con...