Compared to other large engineering projects, geologic repositories for high-level waste present distinctive challenges: 1) they are first-of-a-kind, complex, and long-term projects that must actively manage hazardous materials for many decades; 2) they are expected to hold these hazardous materials passively safe for many millennia after repository closure; 3) they are widely perceived to pose serious risks. As is the case for other complex projects, repository programs should proceed in stages. One Step at a Time focuses on a management approach called adaptive staging as a promising means to develop geologic repositories for high-level radioactive waste such as the proposed repository at Yucca Mountain, Nevada, USA. Adaptive staging is a learn-as-you-go process that enables project managers to continuously re-evaluate and adjust the program in response to new knowledge and stakeholder input. Here, advice is given on how to implement staging during the construction, operation, closure and post-closure phases of a repository program.