Birth cohort, or generation, differences in personality include views of the self (increases in self-esteem, narcissism, assertiveness, and agentic traits, leading to the label ‘Generation Me’) and mental health (externality in locus of control, increases in depressive symptoms). The origins of these trends lie in culture, including changes in women's roles, parenting, media, and social connections. Birth cohort should be considered as an environmental influence on individual personality traits. Challenges to cross-temporal meta-analysis are discussed, including response bias, changes in college populations, data from the University of California campuses with major confounds, sampling issues, and the misperception that the ecological fallacy is committed.