This scoping review seeks to integrate disparate research on the role of similarity in romantic relationships, a topic of long-standing interest among researchers and popular culture alike. We offer a synthesis of 339 articles measuring similarity and relationship outcomes in established romantic relationships. We report trends in extant research regarding domains of similarity, methods of calculating similarity, and sample characteristics. Our findings showed generally mixed results when examining the association between similarity and relationship outcomes. This trend remained consistent across different similarity types and measurement methods, though stronger effects were found for perceived as opposed to actual similarity. Thus, despite popular belief, similarity does not seem to be universally associated with superior relationship outcomes. Future research should incorporate more diverse samples, holistic measures of similarity, and advanced statistical techniques and should explore specific situations where similarity might be crucial.
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