Increased interaction between scientists and the social environment is considered to be one of the characteristics of modern science. This interaction can occur through collaboration between different sectors in society. In connection to this, the Triple Helix model claims that interaction between university, industry and public sectors, is key to modern innovation development. So far, cross-sector interaction between actors in environmental science has been scarcely studied in a scientific manner. Most studies carried out in the area have disregarded the actual practice of such collaborations and what happens in projects where these sectors interact. As this has become a common way to solve environmental problems, it is of considerable importance to gain more knowledge about this process. The objective of this research was to study and explain cross-sector collaboration. Using the interactive research method, characterised by joint learning and interaction with the participants, this was explored through two case studies. The method was well suited for studying ongoing interactions between the university, industry and public sectors. The first case was an international collaboration between representatives of the Triple Helix sectors. Here, olive-mill wastewater in Greece was the focus. The Triple Helix framework was used both on the intended analytical level and at a management level closer to the actor level of the participants. The second case was a three-year environmental research project in the Kalmar region where strong university-industry collaboration was carried out in order to find wastewater treatment solutions in the wood industry. This collaboration was extended to include more actors in the region during the process. The actual practice of these cases showed the importance of a dialogue between participants. Triple Helix can be used as an initial framework for such a dialogue through which the model is redefined by input from all sectors.