1 Four-Worlds Model for Configurable Services Heiskala Mikko, Tiihonen Juha, Anderson Andreas, Soininen Timo Abstract Configurable products are one way to pursue mass customisation. Configurators are information systems that support the repetitive specification of product variants and description of all possi- ble product variants of a configurable product in a configuration model, Configuration models are expressed using concepts and their relationships defined in the conceptual model underlying the configurator. Many different conceptual models exist and there is no dominant approach. The conceptual model significantly affects ease of modelling, understandability, compactness and expressiveness of configuration models as well as computational complexity of computer sup- port. In this paper we present a conceptual model, or conceptualisation, for modelling configura- ble services, an area with relatively little previous research, based on a synthesis of previous work extended with our own experiences with four case companies. Keywords conceptual model; configurable services; configurable products; configurator Contact information Mikko Heiskala, M.Sc. (Tech), Researcher. Laboratory of Work Psychology and Leadership, Department of Industrial Engineering and Management, Helsinki University of Technology, P.O. Box 5500, 02015 HUT, Finland. Mikko.Heiskala@tkk.fi Juha Tiihonen, Lic.Sc. (Tech), Researcher, project manager, Software Business and Engineering Institute, Department of Computer Science and Engineering, Helsinki University of Technology, P.O. Box 9210, 02015 HUT, Finland, Juha.Tiihonen@tkk.fi Andreas Anderson, M.Sc. (Tech), Software Engineer, Variantum Oy, Tekniikantie 14, 02150 Espoo, Finland, andreas.anderson@variantum.com Timo Soininen, Dr. Sc. (Tech), Docent, Software Business and Engineering Institute, Depart- ment of Computer Science and Engineering, Helsinki University of Technology, P.O. Box 9210, 02015 HUT, Finland, timo.soininen@iki.fi