[Correction Notice: An Erratum for this article was reported in Vol 34(6) of Journal of Family Psychology (see record 2020-62946-001). There are two errors in the last sentence of the fifth paragraph (Model 4: Fluctuations in Cumulative Stress X Fluctuations in Behavior) of the Results section whereby the text "less cumulative stress" and "less stress" should have read "more cumulative stress" and "more stress," respectively. Thus, the correct sentence is as follows: "Specifically, relative increases in observed dyadic negativity were associated with decreases in husbands' relationship satisfaction when husbands also experienced more cumulative stress, whereas decreases in observed negativity in the presence of more stress were associated with increases in husbands' satisfaction (t = -2.00, p = .045, see Figure 1 and Table 2, Model 4)." Note that the findings are correctly stated elsewhere in the article.] Although a number of theoretical perspectives in relationship science argue that variability in couples' relationship satisfaction over time is driven by changes in their communication, tests of this hypothesis have been limited to single assessments of behavior. To address this gap, we examine within-couple, across-time changes in communication, and we argue further that couples' external circumstances might combine with these behavioral changes to generate changes in relationship satisfaction. Using self-reports of satisfaction and in-home observational data collected 4 times at 9-month intervals from 414 newlywed couples, we show that fluctuations in dyadic behavior and spousal stress covary with fluctuations in spousal satisfaction. Tests of the interaction between fluctuations in stress and behavior reveal that husbands who experience upward fluctuations in negativity also experience decreases in relationship satisfaction at the same wave but only if they are concurrently experiencing greater stress than usual. Downward fluctuations in problem-solving effectiveness are associated with lower relationship satisfaction but only among spouses who had chronically high levels of cumulative stress; when chronic stress is low, reduced problem-solving effectiveness is unrelated to satisfaction. Exclusive focus on between-couple variability in couple communication, without regard for the stressors that couples face, will likely restrict the understanding and prevention of relationship distress. (PsycInfo Database Record (c) 2020 APA, all rights reserved).