This study examined amount of uncertainty, openness of communication about uncertainty, and the uncertainty reduction process as three competing mechanisms that account for increased intimacy in romantic relationships. To test these competing mechanisms, we used multilevel modeling to analyze longitudinal data that were collected from individuals in romantic associations over a 6-week period. Results of separate analyses indicated that the amount of uncertainty was negatively associated with concurrent intimacy and the openness of communication about uncertainty, and decreases in uncertainty were positively associated with subsequent intimacy. When all three predictors were considered simultaneously, the decrease in uncertainty was the only significant predictor of intimacy. These findings highlight the importance of the uncertainty reduction process, rather than low amounts of uncertainty, for increased intimacy.