This paper sets the context for those that follow in this Special Edition by describing why STEP (Spherical Tokamak for Energy Production) has been launched, what it aims to achieve (benefits) and, principally, how the whole programme will be delivered (strategy).  The paper draws on work on major project delivery and organisation design and applies this to the context of STEP, which is dominated by significant uncertainty in all dimensions (technical, financial, commercial, programmatic), where there is embryonic delivery capability but where there are also global-scale opportunities.  This leads to an approach based on securing and organising the right capability from both public and private sectors to work in a collaborative arrangement with a single purpose and, critically, in an operating model designed to manage uncertainty and emerging risks, and to exploit opportunities.  Placing adaptability at the core of the organisation design, particularly the ability to deliver emergent strategy through guided empowerment in pursuit of an ambitious aim, is a further development beyond much of the current thinking in major projects.  The paper concludes with an appendix which translates that programme approach into principles for managing the engineering design work.