Multi-objective combinatorial optimization for selecting best available techniques (BAT) in the industrial sector: the COMBAT tool The introduction of best available techniques (BAT) with the European Commission’s directive 96/61, created a new framework for ’cleaner’ production in the industrial sector. BATs practically constitute recommended techniques for each of the steps in the manufacturing process. Thus, the industries must decide on which BATs are most appropriate for their processes. In the current study, an integrated approach is applied in order to find the mixture of BATs for the entire industrial sector that satisfies as much as possible the economic and the environmental criteria. The former represent the industry owner’s point of view expressed by the Net Present Value of the projects and the latter represent the society’s point of view quantified by the emission reduction in some major pollutants. The developed multi-objective optimization model is addressed using two methods: (1) goal programming and (2) generation of the Pareto optimal solutions using an augmented version of the $epsilon$-constraint method followed by an interactive filtering process in order to select the most preferred Pareto optimal solution. The generation of the Pareto optimal solutions is performed using an improved version of the widely used $epsilon$-constraint method that overcomes some of its known drawbacks. The COMBAT tool (combinatorial optimization with multiple criteria for BAT selection) that is developed for implementing these methods is also described and the results from its application in the industrial sector of the greater Athens area are presented.