Rumination, the perseverative thinking about one's problems and emotions, is a maladaptive response to sadness and a risk factor for the development and course of depression. A critical challenge hampering attempts to promote more adaptive responses to sadness is that the between-person characteristics associated with the tendency to ruminate following depressed mood remain uncharacterized. We examine the importance of between-person differences in blood-oxygen-level dependent (BOLD) functional networks underlying cognitive control for the moment-to-moment association between sadness and rumination in daily life. We pair functional magnetic resonance imaging with ambulatory assessments measuring momentary sadness and rumination deployed 10 times per day over 4 consecutive days from 58 participants (40 female, mean age = 36.69 years; 29 remitted from a lifetime episode of Major Depression). Using a multilevel model, we show that rumination increases following increases in sadness for participants with higher than average between-network connectivity of the default mode network and the fronto-parietal network. We also show that rumination increases following increases in sadness for participants with lower than average between-network connectivity of the frontoparietal network and the salience network. In addition, we find that the flexibility of the salience network's pattern of connections with brain regions across time is protective against increases in rumination following sadness. Our findings highlight the importance of the neural correlates of cognitive control for understanding maladaptive responses to sadness and also support the value of large-scale functional connectivity networks for understanding cognitive-affective behaviors as they naturally occur during the course of daily life.control where the variables are sample-level parameters and the variables are residual betweenperson differences that may be correlated with one another but are uncorrelated with the variable . Parameters 01 to 09 indicate the effects of person-level default mode network and salience network connectivity, default mode network and fronto-parietal network connectivity, frontoparietal network and salience network connectivity, salience network flexibility, motion, usual sadness, age, sex, and depressive symptoms on rumination. Parameters 11 to 14 indicate how between-person differences in default mode network and salience network connectivity, default mode network and fronto-parietal network connectivity, fronto-parietal network and salience network connectivity, and salience network flexibility moderated the association between the previous moment's sadness on the current moment's rumination. Our simultaneous estimation of multiple cross-level interaction effects (i.e., level 2 variables moderating level 1 variables) provides a parsimonious test of our hypotheses but also follows best-practice recommendations for estimating cross-level interaction effects using multilevel modeling (Aguinis, Gottfreson, & Culpepper, 2013). We ...