This article addresses the absence of a conceptually grounded definition and empirically validated measure of 'Quiet Quitting' — the pattern of employee behavior involving minimal workplace contribution just sufficient to avoid involuntary dismissal. The authors argue that Quiet Quitting is a distinct, multidimensional construct that differs meaningfully from adjacent phenomena such as burnout, turnover intentions, continuance commitment, and psychological contract breach. Through four sequential studies — an MBA student content validation sample, a Prolific panel of U.S. full-time employees (n=985), a global snowball sample across European countries (n=2,128), and a Portuguese field sample of full-time employees (n=1,897) — the authors develop and validate the Multidimensional Quiet Quitting Scale (MQQS), comprising behavioral and emotional dimensions. Key findings indicate that behavioral quiet quitting is negatively associated with interpersonal organizational citizenship behaviors (OCB-I), while emotional quiet quitting is negatively associated with organizational citizenship behaviors (OCB-O) and positively associated with turnover intentions. The authors conclude that the MQQS provides a valid, reliable instrument for future research into the nomological network, antecedents, and consequences of quiet quitting across organizational contexts. Key insights: Quiet Quitting is conceptualized as a two-dimensional construct comprising a behavioral dimension (deliberate restriction of effort to the minimum necessary to avoid dismissal) and an emotional dimension (comfort and satisfaction with that minimal contribution level), distinguishing it from burnout, turnover intentions, continuance commitment, and psychological contract breach. Across three field samples, behavioral quiet quitting was consistently negatively associated with interpersonal organizational citizenship behaviors (OCB-I), while emotional quiet quitting was more strongly associated with reduced OCB-O and heightened turnover intentions, suggesting the two dimensions carry distinct predictive profiles. The MQQS demonstrated acceptable psychometric properties — including internal consistency, factor structure, and nomological validity — across culturally diverse samples spanning the United States, 33 European countries, and Portugal, though cross-cultural variations in the prevalence and expression of quiet quitting remain an open empirical question. Practical takeaways: Organizations and researchers now have access to a validated 13-item scale (MQQS) that can be used to measure quiet quitting separately from related constructs such as commitment, burnout, or turnover intentions, enabling more precise diagnostic assessment of this behavioral pattern. The differentiated predictive validity of the behavioral and emotional dimensions suggests that interventions targeting withdrawal may need to address both the observable restriction of effort and the underlying affective comfort employees associate with minimal contribution — these may require distinct managerial responses.