Product-Service Systems (PSS) were developed as more sustainable alternatives to traditional product sales, especially through better and more intensive use of materials. Some companies currently use this business model successfully, while others are still in the process of transforming to PSS. The change from providing a product to providing a service has proved to be rather difficult and actual sustainable benefits have been questioned. The research described in this paper was part of the ServINNOV project.The initial idea was to find out if, and how, indicators could help in the move to PSS. Indicators could give a clearer picture of the situation and monitor progress during the transition period. Indicators could also help companies focus on their core activities, and determine whether a PSS offering really helps them to become more sustainable. The study covers an overall view of sustainable indicators, with a focus on environmental issues. The research for this paper was carried out through both theoretical and empirical studies. Empirical findings were obtained from interviews with three companies, all of them working with PSS on different levels. The results will guide transition to provide more sustainable PSS.