This thesis scrutinize the insight from emerging theories on cooperation in common-pool resources. The models of co-management were inspired by examples of collective action among people, which is in stark contrast to the prominent tragedy of commons metaphor. The focus in this thesis is on the effect of technological change on the co-management of a natural renewable resource. The fishery of Lofoten is explored during the years 1864–1988, as this fishery has been regarded as an example of successful co-management. It had for instance a local governance structure that integrated the fishermen into the decision making process. Furthermore, the fishery of Lofoten is well documented with the annual Lofoten reports ( Lofotberetningene ). The data set is extracted from these unique historical documents. During the years of 1905–1920, a rapid technological progress occurred as the share of motorized vessels increased from 0 to 40 per cent. This period coincide with increasing violations of the co-management rules and regulations. A regression model is used to measure these violations, which serves as a proxy for defection in the co-management. The result shows that a shock in motorization was associated with a strong and significant effect on violations of the rules and regulations. Furthermore, it suggests that technological change affects the cooperation of a common-pool resource. The strain on cooperation would then increase because of the chances of higher effort and gear conflicts in the fishery, due to higher mobility and speed. The findings encompass the emerging theories, and it shows that a rapid technological change is associated with a significant eroding cooperation in a common-pool resource. It shows that the pressure towards stronger monitoring and enforcement is associated with increasing technological progress.