This PhD thesis explores mass customized service level agreements (SLAs) and is to be considered as a study in mass customized services related to physical products. The overall goal of this thesis has been to extend the research carried out at DTU Management to also include services – more specifically by extending the already existing method applied for the development of configuration systems, “The Procedure for developing configuration systems”. As the literature on mass customized services is, in general, very limited, the approach has been to identify the essential elements of the respective fields (services, SLAs, mass customization) having served as the basis for carrying out exploratory studies, which has resulted in two concrete case studies carried out at two different companies. The aim of the research project has partly been to elucidate the field of mass customized services and partly to create a tool that can support companies in the handling of so-called product solutions (product & service), based on the company strategy of Mass Customization. The research work of this PhD thesis demonstrates the common problems encountered by service organisations in connection with the sales and delivery of services. Problems which, among other things, are connected to the characteristics that make services different from tangible products (intangible, difficult to standardise, simultaneous production/ consumption and perishable). Generally seen, some of the most difficult problems encountered are related to the issue of defining services, which in the end is of importance for the quality of the service delivered (explained by customer-satisfaction). The thesis describes how to model a product range, which can be used for the specification of the services included in a Service Level Agreement. In addition, the PhD thesis describes how mass customized services can minimize the identified problems related to the sales and delivery of services, including the advantages/disadvantages observed. The thesis is first and foremost to be considered as a further development of the already existing research work carried out at DTU Management and a contribution to the understanding of the problems related to the development of configuration systems for services. At the same time, it must be noted that the thesis is also a general contribution to the understanding of the general field of mass customized services.