Recent findings highlight the limited agreement between diagnostic ratings provided by practicing clinicians and the self-report and interview methods typically employed in research settings. Such discrepancies between the diagnoses assigned in research and applied settings greatly complicate the translation of empirical findings into practice. This review highlights these disagreements, offers explanations for these observed differences, and provides 5 implications for research. Specifically, we provide evidence that, despite criticisms, self-reported psychopathology may be at least as valid as clinicians’ unstructured diagnoses. Further, we highlight the need for research that provides clinicians with the most valid tools, including those that focus on dimensional constructs, rather than diagnostic categories. In addition, we recommend that adult psychopathology research incorporate methodologies from general personality for unraveling informant discrepancies. We highlight recent work that has provided valuable tools for incorporating metaperception—the extent to which one is aware of how they are perceived by others—for contextualizing these differences. We also underscore the utility of emerging technologies that provide rich data, such as ambulatory assessment, for overcoming the criterion problem. Finally, we recommend that advances in combining data from multiple sources from the childhood psychopathology literature, such as examining the extent to which discrepancies themselves might aid in diagnosis, be incorporated into adult psychopathology research. In sum, we hope that these implications inspire research that improves the science of diagnostic assessment in a way that might ultimately improve practice.