Definitional and conceptual problems in research on psychological aggression involve inconsistencies in defining what behaviors/actions constitute psychological aggression in an intimate relationship. Associated problems include assumptions that current measures of psychological aggression accurately assess a person's experience of psychological abuse; awkward application of physical-abuse models to this more complex phenomenon; and varied language used by researchers, theorists, and practitioners. Methodological problems in the research not only result directly from problems in conceptualization but also arise from many other sources. Researchers have typically approached the measurement of this complex abusive interaction by collecting self-report information from one member of a couple regarding whether certain behaviors (designated by the researchers as psychological abuse) have occurred. The validity of this approach is highly questionable. This article outlines a number of factors that undermine the validity of this research approach, including the context in which a behavior occurred, whether the recipient of the behavior viewed it as "abusive," and whether the language used on researchers' checklists of behaviors was interpreted similarly by all respondents. Although a number of published articles report adverse effects due to experiencing psychological aggression, the relatively small number of studies, the problematic methodology, and the typical co-occurrence of physical violence prevent strong statements of causal effect or clear, uncontested results. Probably due to methodological issues, contradictory results are often found. This article advises that a more significant impact for research in this field is likely to come from intensive study of long-term, enduring patterns of serious psychological abuse, with attention to implications for effective treatment and prevention. 54 references