The current negotiations on non-agricultural market access for developing countries involve ambitious tariff-cutting formulas combined with exceptions or “flexibilities” for some products. The resulting complexity makes it difficult to be sure what the effects of “modalities” would be. We develop a political-economy model to understand the support for the current tariff regime, and hence the political costs of alternative approaches to tariff cutting. We then use this model to assess countries’ likely choices of flexibility options, and the implications for tariffs if the proposed modalities under recent discussion were implemented.