Restoration ecology is a discipline whose time has come. In recent years it has advanced almost explosively on a range of fronts, with attempts to restore habitats, species and human cultural values. We view it as timely to try and provide researchers and practitioners with a comprehensive review – the ‘state of the science’, shortly after the turn of the century. The increasing need for ecological restoration is an inevitable consequence of the relentless growth of the global human population, its increasing cultural and technological sophistication and the concomitant consumption of resources. Our central aspiration to understand ecosystems sufficiently well to be able to restore or replace them may be regarded with dismay by those who believe that it will serve to encourage destruction in the first place. However, any knowledge potentially can be abused and the benefits of restoration surely greatly outweigh any abuse. Clearly, at any site, conservation of the existing organisms in their undamaged environment is unequivocally preferable to subsequent restoration in situ, or reconstruction of an equivalent system elsewhere by way of mitigation. Unfortunately, conservation cannot always be wholly successful and so long as its effectiveness is less than perfect, the world's biodiversity is on an inexorable ‘ratchet’ to extinction; the main uncertainty is the rate at which this will happen, and restoration will be the only means to counteract the decline.