Implementing sustainability in business is steadily gaining more attention. A growing number of companies currently work on the implementation of sustainable criteria in the design related departments and their design processes. Although theory and methods are available, practice shows that this integration process of sustainability criteria is not straightforward. In this paper, different cases from practice are described based on a study of five Flemish and three Dutch firms that are broadening their (sometimes already extensive) experience on this implementation process. The emphasis of this paper is put on influential factors such as the presence of an implementation process of sustainability criteria inside a firm’s product development department, with a focus on the need for a sustainability vision and strategy, resistance against sustainability and the link between internal communication and resistance. Our data suggest that a clear vision, mission, strategy and planning of the implementation process of sustainability criteria are needed, but not necessarily from the beginning of the process. Apart from that, factors of resistance appear to evolve throughout the implementation process that vary in nature (organizational versus personal) and content. Lastly, three types of communication are suggested that need to be considered and applied in order to involve, support and inform employees in order to positively progress into the direction of more sustainable products and processes.