In this article, we present the new multiregional global MARKAL-TIMES1 model and on several recent applications to global energyenvironment issues. The development of the model was motivated by the need to analyze international energy and environmental issues such as climate change, using a detailed, technology rich modeling framework. We then present three different types of application. First, the model is applied to conduct the cost-effectiveness analysis of Greenhouse Gas (GHG) emission abatement, whereby constraints on COn emissions are added to the base case formulation. The model then computes the cost-efficient response of the energy system to these emission targets. Second, we address the issue of "who pays"' for emission reductions (whereas the cost-effictiveness analysis addressed the "who acts" issue). More precisely, we use the model to devise and evaluate certain allocation rules for attributing initial emission rights to regions in a cap-and-trade system. Third, we use World MARKAL in a cost-benefit mode, i.e. we augment the model with damage costs resulting from climate change, and run the integrated model without any pre-set tarlThe applications reported here were made with a MARKAL model. The TIMES incarnation was developed more recently and wil! progressively replace MARKAL in future applications. The two models share many features, including those deiscussed here. In addition, TIMES incorporates new features that are briefly discussed in the Appendix.