Traditional public finance theory may be applied to the internalization of international environmental externalities. The policy constraint imposed by the absence of sovereign international government may be partially overcome through international environmental agreements. Instruments such as cost sharing, found in existing agreements, are generally unsophisticated. Two proposals entailing improved instruments are considered: (a) an international carbon tax, and (b) a global commons trust fund financed by earmarked excise taxes or charges. Political realities appear to preclude the early adoption of sophisticated international environmental taxes, but modest improvements in the design and implementation of existing instruments may be feasible.