Owing to the wide range of trigeneration systems suitable for small-scale applications, the selection of the optimal system according to the end users' requirements and environmental conditions is crucial. The evaluation and comparison of possible alternatives of trigeneration systems are a multi-criteria decision problem because not only economic aspects must be considered but also technical, environmental and social aspects. This paper presents the case of selection of a trigeneration system for a typical residential building. Several kinds of trigeneration systems, whose dynamical sources are Stirling engines, micro-turbines, reciprocating engines and fuel cells, respectively, and a separate generation system are evaluated and compared in detail. As the evaluation criteria are a mixture of quantitative and qualitative criteria, quantitative multi-criteria methods are inadequate for handling this type of problems. Therefore a multi-criteria decision-making method, which combines the subjectivity of decision maker and the objectivity of numerical data, based on Fuzzy Set Theory and Analytic Hierarchy Process is proposed to solve this selection problem. Copyright (C) 2010 John Wiley & Sons, Ltd.