The international standards on portfolio, programme and project management (ISO 21500, 21503, 21504 and 21505) and on system engineering (ISO 15288) do not include a definition of ‘quality’ as ISO has a policy not to define words where a ‘plain English’ dictionary definition exists and serves the need. Quality planning and assurance are concerned with the way work is managed and carried out, aiming to ensure there are no defects (or minimum acceptable defects) in the first place; fixing defects can be expensive. It is estimated that the later an error is detected, the more costly it is to rectify with some researchers claiming that rectifying a software error during live running is 100 times more costly than the same error if detected during design. Different deliverables lend themselves to different methods of verification and, in some cases, the methods can be combined.