Genome editing - a suite of methods for creating changes in DNA more accurately and flexibly than previous approaches - was hailed as the 2011 Method of the Year by Nature Methods, and the CRISPR/Cas9 system of genome editing was named the 2015 Breakthrough of the Year by Science. The technology has excited interest across the globe because of the insights it may offer into fundamental biological processes and the advances it may bring to human health. But with these advances come many questions, about the technical aspects of achieving desired results while avoiding unwanted effects, and about a range of uses that may include not only healing the sick, but also preventing disease in ourselves and future generations, or even altering traits unrelated to health needs. Now is the time to consider these questions. Clinical trials using edited human somatic cells are already underway and more are already anticipated. To help direct the use of genome editing toward broadly promoting human wellbeing, it is important to examine the scientific, ethical, and social issues it raises, and assess the capacity of governance systems to ensure its responsible development and use. Doing this also entails articulating the larger principles that should underlie such systems.