The awareness of environmental impacts lead to that organizations are starting to work towards UN's global sustainability goals. To influence customers into a more sustainable behaviour, organizations have the potential to look at nudging as a tool. A nudge is a way to alter peoples behaviour into taking a certain decision. However, since many organizations offer their service or product in the digital environment, such as websites or apps, increased knowledge of digital nudging is required. This thesis aims to establish a framework for how nudges should be designed and used on digital platforms to encourage sustainable decisions. The purpose is to enlighten designers of digital environment of the potential of nudges, pitfalls to avoid, and a general design process to follow. The framework is based on a literature study and interviews with people familiar with the concept of nudging. To examine how the framework works a case study is performed, this includes a workshop, performing a user research, developing prototypes and finally, conduct user tests. By testing the framework further methods could be found, this meant that more practical steps could be included in the framework. The result of this thesis shows that the framework proved to be useful and functional to use when designing digital nudges to encourage sustainable decisions.