With Initial Operating Capability (IOC) declared by the US Marine Corps and US Air Force, increasing production and delivery rates, and impressive performances in recent exercises, the F-35 programme and the fifth-generation capability that it represents look to have turned a corner. As the capability moves towards Full Operating Capability (FOC), the debate, so long focused on costs, delays and technical issues, should now begin to be framed in new terms. André Adamson and Matthew Snyder analyse some of the stakes involved as the capability increasingly acts as a driver for fifth-generation transformation, and to consider some of the implications for air forces that have committed to the programme and, perhaps more significantly, for those that have not.