A model of judgment maintenance and change is proposed that specifies the various processes that take place at the time of making a judgment on the basis of memory-based and online information. This model proposes that attitude maintenance and change depend on three processes: recalling a prior attitude, recalling or receiving other attitude-related information, and comparing the prior attitude with attitude-related information. Unlike prior models, the activation/comparison model assumes that all three processes can elicit attitude change and maintenance under different conditions. For instance, the mere activation of attitude-related information that is consistent with a prior attitude will favor stability, whereas activation accompanied with comparison with a prior attitude will result in polarization of the prior attitude. Furthermore, even when prior attitude accessibility will elicit attitude maintenance in the absence of comparative processes, prior attitude accessibility can accelerate comparison and therefore change when comparative cures are present. Finally, people who are motivated to compare their prior attitudes with new information should by necessity first activate their prior attitude before comparison can take place. Consequently, attitude comparison cues may induce attitude survival if subsequent processing stops at the point of attitude activation and does not proceed to the stage of attitude comparison. Comparative principles are identified and the implications of this model are discussed in relation to prior theorizing on change in attitudes and nonevaluative judgments.