A meta-analysis of 128 studies examined the effects of extrinsic rewards on intrinsic motivation. As predicted, engagement-contingent, completion-contingent, and performance-contingent rewards significantly undermined free-choice intrinsic motivation (d = -0.40, -0.36, and -0.28, respectively), as did all rewards, all tangible rewards, and all expected rewards. Engagement-contingent and completioncontingent rewards also significantly undermined self-reported interest (d = -0.15, and -0.17), as did all tangible rewards and all expected rewards. Positive feedback enhanced both free-choice behavior (d = 0.33) and self-reported interest (d = 0.31). Tangible rewards tended to be more detrimental for children than college students, and verbal rewards tended to be less enhancing for children than college students. The authors review 4 previous meta-analyses of this literature and detail how this study's methods, analyses, and results differed from the previous ones.By 1971, hundreds of studies within the operant tradition (Skinner, 1953) had established that extrinsic rewards can control behavior. When administered closely subsequent to a behavior, rewards were reliably found to increase the likelihood that the behavior would be emitted again, an effect that persisted as long as the reward contingency was operative. When rewards were terminated, the likelihood that the behavior would be emitted eventually returned to the prereward baseline. This general finding led to the widespread advocacy of rewards as a motivational strategy, and behavior-change programs based heavily on the use of rewards were introduced into a variety of applied settings.In 1971, Deci (1971 argued that some activities provide their own inherent reward, so motivation for these activities is not dependent on external rewards. In line with White (1959), Deci referred to such activities as intrinsically motivated and raised the question of how extrinsic rewards would affect people's intrinsic motivation for these activities. Research reported in that and subsequent papers (Deci, 1971(Deci, , 1972a(Deci, , 1972b revealed that tangible rewards (viz., money) could undermine college students' intrinsic