Conflicts may drift from one family dyad to another. Short-term spillover and long-term transmission processes suggest that interparental conflict will cause parent-adolescent conflict, and vice versa, as well as that negative mood of parents and adolescents may be one of the transferring mechanisms. This multi-informant daily diary study is among the first to test the day-to-day and year-to-year cross-lagged effects between interparental conflict and later parent-child conflict at the level of individual families (as compared to between-family studies). Also, this study investigated the mediating role of negative mood. Data came from 443 Dutch adolescents (M = 13.02, 44.5% girls) and their mothers. A total of 75 daily diaries regarding conflict and negative mood were completed across 15 weeks spread over 5 years. Random-intercept cross-lagged panel models were applied to investigate long-term year-to-year transmission, and Dynamic Structural Equation Modeling was used to investigate short-term day-to-day spillover. Overall, we found neither short-term spillover, nor long-term transmission, as the reciprocal cross-lagged effects between interparental conflict and adolescent-mother conflict were nonsignificant. Even though we found direct and reciprocal cross-lagged effects between negative mood and both interparental and adolescent-mother conflict on both the day-to-day and year-to-year timescales, both the direct and the indirect effects between interparental and adolescent-mother conflict were nonsignificant. (PsycINFO Database Record (c) 2020 APA, all rights reserved).