Objective: Quality of life of people with dementia and their family carers is strongly influenced by interpersonal issues and personal resources. In this context, relationship quality (RQ) and sense of coherence (SOC) potentially protect and promote health. We aimed to identify what influences RQ in dyads of people with dementia and their carers and to examine differences in their perspectives. Methods: Cross-sectional data were used from the Actifcare cohort study of 451 community-dwelling people with dementia and their primary carers in eight European countries. Comprehensive assessments included the Positive Affect Index (RQ) and the Orientation to Life Questionnaire (SOC). Results: Regression analyses revealed that RQ as perceived by people with dementia was associated with carer education, stress, and spouse caregiving. RQ as perceived by carers was associated with carer stress, depression, being a spouse, social support, reported neuropsychiatric symptoms of dementia, and carer SOC. Neuropsychiatric symptoms and carer stress contributed to discrepancies in RQ ratings within the dyad. The only factor associated with both individual RQ ratings and discrepancies was carer stress (negative feelings subscore). No significant differences in the overall perception of RQ were evident between spouses and adult children carers, but RQ determinants differed between the two. Conclusions: In this European sample, carer SOC was associated with carer-reported RQ. RQ determinants differed according to the perspective considered (person with dementia or carer) and carer subgroup. A deeper understanding of RQ and its determinants will help to tailor interventions that address these distinct perspectives and potentially improve dementia outcomes.