This article examines the influence of the Millon Clinical Multiaxial Inventory (MCMI) as a clinical and research instrument beyond the borders of the United States. The MCMI's theoretical and empirical grounding, its alignment with the Diagnostic and Statistical Manual of Mental Disorders (DSM), and scales that can be interpreted both categorically and dimensionally, are the primary features that make the test attractive. We begin with studies that evaluated the construct equivalence of the different language adaptations. Data from the most widely researched non English-language forms (Danish, Dutch, and Spanish) show excellent comparability with Millon's original. Nevertheless, significant problems were noted in efforts to create clinical groups that would allow for equivalence of diagnostic accuracy when using the cutoff scores. Although dimensional aspects of the scale scores were not affected by this, the adapted measures might show attenuated diagnostic accuracy compared with Millon's original. Next, we present MCMI studies conducted in clinical settings to document where the adapted tests have made their greatest impact in the international literature. A wide variety of clinical applications demonstrated broad utility, and given the high number of issues addressed, we think Millon's influence will certainly stand the test of time in different domains and settings.