This chapter reviews evidence about Agreeableness and antagonism and their association with mental health across cultures. Agreeableness is a personality dimension defined in a Western context, but which corresponds to a reasonable degree with indigenous dimensions found in other cultural settings. Studies translating Western measures into other languages have found similar factor structures, but not evidence for scalar measurement invariance, which would allow for reliable comparison of scores across cultural and linguistic settings. Interestingly, however, lower average scores for men versus women appear to be more pronounced in industrialized nations with greater gender equity. Agreeableness appears to increase with age across cultures, in particular around the time of taking on adult financial responsibilities. The symptoms and disorders associated with antagonism, including conduct disorder, aggression, psychopathy, antisocial personality disorder, substance use disorders, and borderline personality disorder, generally appear to be globally comprehensible and diagnosable. However, specific symptom patterns can vary considerably, and rates of aggressive behavior and related symptoms appear to be more common in individualistic, industrialized cultures.