Making a societal transition towards sustainability is a global concern of ever increasing urgency. Succeeding in this mission requires all societal sectors to be on board and contribute. This thesis focuses on the transformation of the corporate sector, namely how Internal Corporate Communication (ICC), i.e. communication between senior management and employees, can be designed to engage employees in working with sustainability. This thesis uses a conceptual model developed for ICC and employee engagement and applies it in the specific context of ICC with regards to sustainability in medium- to large-sized companies in Northern Europe. Through interviewing practitioners working with ICC on sustainability in ‘model’ sustainability companies, the research aims to discern best practices on how to design ICC about sustainability to engage employees. The results show that ICC can be a useful tool when it comes to engaging employees in working with sustainability, and the findings are summarized as guidelines for content creation and methods to use to facilitate engagement creation for sustainability. The discussion elaborates on how these guidelines can be used together with the Strategic Sustainable Development approach to facilitate companies’ journeys towards sustainability.