Ecosystems provide multiple ecosystem services to society. Ignoring the multi-functionality of land systems in natural resource management generates potentially trade-offs with respect to the provisioning of ecosystem services. Understanding relationships between ecosystem services can therefore help to minimize undesired trade-offs and enhance synergies. The research on relationships between ecosystem services has recently gained increasing attention in the scientific community. However, a synthesis on existing knowledge and knowledge gaps is missing so far. We analyzed 67 case studies that studied 476 pairwise combinations of ecosystem services. The relationships between these pairs of ecosystem services were classified into three categories: "tradeo ff", "synergy" or "no-effect". Most pairs of ecosystem services (74%) had a clear association with one category: the majority of case studies reported similar relationships for pairs of ecosystem services. A synergistic relationship was dominant between different regulating services and between different cultural services, whereas the relationship between regulating and provisioning services was trade-off dominated. Increases in cultural services did not influence provisioning services ("no-effect"). We further analyzed the pattern of relationships between ecosystem services across scales, land system archetypes and methods used to determine the relationship. Our analysis showed that the overall pattern of relationships between ecosystem services did not change significantly with scale and land system archetypes. However, some pairs of ecosystem services showed changes in relationships with scale. The choice of methods used to determine the relationship had an effect on the direction of the relationship: studies that employed correlation coefficients showed an increased probability to identify no-effect relationships, whereas descriptive methods had a higher probability of identifying trade-offs. The regional scale was the most commonly considered, and case studies were biased among different land system archetypes which might affect our ability to find the effect of scale or land system archetypes on the pattern of relationships. Our results provide helpful information of which services to include in ecosystem services assessments for the scientific community as well as for practitioners. Furthermore, they allow a first check if critical trade-offs have been considered in an analysis.