Public spending has effects which are complex to trace and difficult to quantify. But the composition of public expenditure has become the key instrument by which development agencies seek to promote economic development. In recent years, the development assistance to heavily indebted poor countries (HIPCs) has been made conditional on increased expenditure on categories that are thought to be "pro-poor". This paper responds to the growing concern being expressed about the conceptual foundations and the empirical basis for the belief that poverty can be reduced through targeted public spending. While it is widely accepted that growth and redistribution are important sources of reduction in absolute poverty, a review of the literature confirms the lack of an appropriate theoretical framework for assessing the impact of public spending on growth as well as poverty. There is a need to combine principles of both public economics and growth theory to develop appropriate theoretical guidance for public expenditure policy. This paper identifies a number of approaches that are beginning to address this gap. Building on these approaches, it proposes a framework that has its foundation in a broadly articulated development strategy and its economic goals such as growth, equity, and poverty reduction. It recommends the use of public economics principles to clarify the roles of the private and public sectors and to recognize the complementarity of spending, taxation, and regulatory instruments available to affect public policy. With regard to the impact of any given type of public spending, policy recommendations must be tailored to countries and be based on empirical analysis that takes account of the lags and leads in their effects on equity and growth and ultimately on poverty. The paper sketches out such a framework as the first step in what will have to be a longer-term research agenda to provide theoretically and empirically robust and verifiable guidance to public spending policy.