Purpose – The purpose of this study is to build a generic model for relational development of a value proposition for a service concept. The study seeks to answer two questions: First, what kind of process is practical for joint development of a service concept in customer–service provider collaboration? Second, what are the functional principles for such collaboration? Design/methodology/approach – A participative, design science approach was used to develop the model for a joint-development process. Researchers developed and analyzed joint activities between a provider of industrial maintenance service solutions and its customer during the process of co-developing a service concept for factory maintenance. Findings – The study suggests that a co-development process has to integrate service blueprinting, a stage-gate philosophy, dialogical interaction principles and elements of joint learning to meet the requirement for both efficiency and relationality. Research limitations/implications – The study develops a generic model for collaborative development of value propositions that integrates the aforementioned elements of separate streams of research. Applying the developed model to different contexts would further verify and enhance it. Practical implications – The model can be applied to the development of a value proposition in different collaborative development situations to enhance interplay between efficiency and relationality. Originality/value – The study illustrates a generic model for joint service concept development and proposes a solution balancing contradictory requirements in such a collaboration.