While somatic cell editing to treat disease is widely accepted, the use of human genome editing for “enhancement” remains contested. Scientists and policy-makers routinely cite the prospect of enhancement as a salient ethical challenge for human genome editing research. If preventive genome editing projects are perceived as pursuing human enhancement, they could face heightened barriers to scientific, public, and regulatory approval. This article outlines what we call “preventive strengthening research” (or “PSR”) to explore, through this example, how working to strengthen (...) individuals’ resistance to disease beyond what biomedicine considers to be the human functional range may be interpreted as pursuing human enhancement. Those involved in developing guidance for PSR will need to navigate the interface between preventive goals and enhancement implications. This article identifies and critiques three of these ideas in the interest of anticipating the wider emergence of PSR and the need for a normative approach for its pursuit. All three “candidate criteria” merit attention, but each also faces challenges that will need to be addressed as further research policy is developed. (shrink)