Industrial symbiosis (IS) is becoming a prominent inter-organizational approach for improved resources utilization and reduced emissions. IS literature and development efforts focus on interventions needed to overcome or eliminate various barriers, but pay inadequate attention to paradoxes that cannot be suppressed over time and require management. This study combines literature on paradox theory and IS, exploring the identification and management of paradoxical tensions in eight case studies. The results show that IS relationships trigger paradoxical tensions at the strategic and operational levels, surfaced within and between the organizations. These tensions seem to emerge from, and connected to, the persistence of a cooperation-competition paradox within organizations, when engaging with IS partners contradicts with an organization's competitiveness on the market. The study also provides insights into paradoxical tension management within and between organizations in IS relationships by, for example, shifting partner expectations in favor of IS development, separating responsibilities for IS and core activities between departments, or addressing diverging objectives between partners over time. Both at organizational and inter-organizational levels open dialogue, transparency, and collaboration appear to play key roles in tension management. The study emphasizes the pivotal role of active paradoxical tension management-both internally at strategic and operational levels and externally with partners and facilitators.