This article examines how the exemplars of ideal theory have addressed what I term 'the problem of preservation'. The 'problem' in question is not so much that a political community must make provisions for its self-preservation, but rather that its provisions must correspond to the intentions and capabilities of its neighbours. This constraint implies that the ability of a political community to pursue ideals rather than power depends heavily on who its neighbours happen to be. This article shows how Aristotle, Rousseau, Kant, and Rawls address this problem by recommending measures such as defensive fortification, collective security, and democratic peace, which, they claim, will dampen the anarchic nature of the international system. It argues that the implausibility of these measures renders the ability of political communities to heed the moral guidance offered by ideal theory contingent at best and impractical at worst. If proponents of ideal theory wish to resist this conclusion, then they must offer a more persuasive answer to the problem of preservation.An ideal theory, as I use the term here, is a theory that explains how actual political communities ought to conduct their politics by examining how a political community that finds itself in ideal circumstances would conduct its politics. The practicality of such a theory is brought into question, understandably enough, by the fact that actual political communities tend to operate in less than ideal circumstances. Above all else, actual political communities are confronted by an 'anarchic' international system where the absence of a power able to enforce mutually agreed upon rules leaves all concerned responsible for ensuring their own security and safety. 1 Under the circumstances the mantle of practicality is usually worn by a rather different theory, namely, the political realism associated most famously with Machiavelli. This theory, as Pierre Hassner has put it, emerges when political experience leads the philosopher to settle 'down on the battlefield and base his thinking not on peace but on war, not on the idea of the good society but on the reality of the struggle for power.' 2 * I am deeply grateful to Anna Stilz, Terry Nardin, Melissa Lane, Richard Tuck, and the two anonymous referees for their helpful comments and advice. I am solely responsible for any errors that remain.