Körner, RobertRobertKörner0000-0001-8793-0830Gauglitz, Iris K.Iris K.Gauglitz0000-0002-6500-69782026-05-042026-05-042026https://fis.uni-bamberg.de/handle/uniba/114937Assessing relationship satisfaction—as an outcome, predictor, or control variable—is almost mandatory in studies on romantic relationships. This research was aimed at testing the psychometric properties of the German version of the Couple Satisfaction Index-4 (GCSI-4) by obtaining validity evidence based on internal structure, measurement invariance, and relationships with other variables. Data from five samples (Ntotal = 1526), including individuals and couples in romantic relationships of diverse sexual orientations, were analyzed. Across samples, we found excellent model fit in confirmatory factor analyses, high reliabilities, and good evidence for convergent and discriminant validity. Further, the scale scores were measurement invariant across gender and sexual orientation. Nomological validity was supported by examining intrapersonal and interpersonal links with 43 constructs, ranging from self-related dispositions, relational beliefs, love and well-being, influence and coercive decision-making, as well as relationship behaviors. Criterion validity was demonstrated through negative links with conflict frequency and intentions to engage in infidelity. Altogether, these findings support the good psychometric properties of the GCSI-4 and broaden the validity testing of the CSI in general. We encourage researchers to adopt the GCSI-4 as a reliable and valid instrument for assessing relationship satisfaction in German-speaking samples.engCSIrelationship satisfactionBeziehungszufriedenheitAPIMCFAcouplesmeasurement invariancearticleurn:nbn:de:bvb:473-irb-114937x