Start-ups face several issues and challenges in the course of their development as a compa-ny. Open innovation has been discussed in research for more than a decade as a concept, which can bring benefits to a company. Even though most of the research has been focus-ing on large enterprises, some researchers discuss also benefits for small companies like start-ups. Nevertheless, it can be observed that some start-ups decide to adopt the opposite of open innovation, namely closed innovation, through not sharing internal knowledge to the outside world. Hence, start-ups perceive the benefits of open innovation differently and decide accordingly whether to adopt open innovation or not. The purpose of this study is to explore if start-ups decide to actually do the former and what reasons they have to do so. Therefore, this study will further discover at what point in the development of their start-up and with whom they adopt open innovation. As an attractive industry for start-ups, the mobile services industry is selected as a scope for this study. Furthermore, Sweden is selected as the country of study, due to its reputation as one of the most innova-tive countries in the world. A qualitative study has been conducted using in-depth interviews with founders and co-founders of start-ups to retrieve narrative stories about their start-up’s development from the first day of an idea to a scalable business, and their experiences and motivations in re-gards to the application of open innovation practices. The analysis of this study detects pat-terns among the interviewed start-ups and concludes that start-ups in the mobile services industry in Sweden adopt open innovation in each phase of their development process. Furthermore, these patterns include several reasons why the start-ups applied open innova-tion practices and with whom, which are changing over the course of their development.