The ASPEN software (Analyse des Systèmes de Permis d'Emission Négociables) is dedicated to the analysis of tradable emission permit systems and has been developed for the French Ministry of Environment. ASPEN allows to process Marginal Abatement Cost Curves produced by larger models, in order to compute the market equilibrium price and the quantities exchanged by each partner for different market configurations. Among the different possibilities that can be tested with the ASPEN software are the following : market size by selection of countries regions, changes in "assigned amounts", supplementarity conditions, minimum internal carbon value, minimum international permit price … A set of graphs allows to clearly illustrate the consequences of the different options. The current ASPENd version also allows to change the time horizon for the permit market (2010 or 2030) and the corresponding country targets. This version uses the MAC curves produced with the IEPE's POLES world energy model. It can be installed on any computer by downloading the Aspen_EN.exe (English) or Aspen_FR.exe (Français) files (just click on the appropriate image below) and then by double-clicking on the program's icon.