Sustainable use of the planet will require multiple sustainability strategies, which will range from the entire system, the entire Earth, the local or regional. Strategies starting at the highest system level are referred to as 'top-down', and strategies designed for components, local or regional, are referred to as 'bottom-up'. Doubtless, several intermediate levels will eventually be required, although the number is far from clear at this time. It is abundantly clear that both top-down and bottom-up strategies must be integrated effectively or neither will work well. Furthermore, there will be significant uncertainties at both levels of organisation, which will be reduced as evidence accumulates. However, sustainability is too complex and dynamic to reduce scientific uncertainty to a level desired by most decision makers. A great emphasis on sustain-ethics and value judgements will improve communications between those working at different organisational levels since humankind's wish to leave a habitable planet for its descendants and those of other life forms is clearly a value judgement.