This paper argues that while sources of potential discipline over domestic macro economic policies such as pegged exchange rates, high capital mobility, and IMF policy conditionality are commonly viewed as constraints, it is usually more productive to view them as influencing incentive structures in a world of multiple relevant actors. From this perspective, pegged, as opposed to genuinely fixed exchange rates, are typically not an adequate substitute for domestic discipline enhancing measures. The micro level political economy analysis presented suggests serious limits to the effectiveness of external strategies as sources of discipline. Indeed, their effects can sometimes be perverse. For example, high capital mobility under fixed exchange rates can reduce short run discipline over fiscal policy and impede the ability of an independent central bank to counteract political business cycles in fiscal policy. The analysis highlights the problems of attempting to use commitment devices with asymmetric time profiles to overcome problems generated by the asymmetric short run effects of discretionary monetary and fiscal policies. In particular exchange rate pegging gives front loaded benefits and delayed costs. This makes for a particularly inefficient strategy for trying to avoid domestic macro economic time inconsistency problems. Where short time horizons greatly discount the prospective future costs of a currency crisis, the political incentives generated by pegged rates often fail to provide sufficient monetary and fiscal restraint to avoid such crises. They also tend to discourage the prompt adjustment of disequilibrium exchange rates. As a consequence, exit from a pegged regime is often delayed too long and currency crises result. Thus the political incentive structures generated by exchange rate pegging can be as great a source of difficulty for the smooth operation of intermediate exchange rate regimes as are the economic forces of high capital mobility stressed by many economists. The overall thrust of this paper is to suggest that external sources of discipline over macroeconomic policies are often weak and sometimes perverse. For many, and perhaps most countries, the primary focus for discipline should be internal.