Guided primarily by life history theory, this study was designed to identify how and why early exposure to caregiver intimate relationship instability uniquely predicts children's externalizing symptoms in the context of other dimensions of unpredictability characterized by residential and parental job transitions. Participants included 243 preschool children (Mage = 4.60 years) and their mothers who participated in 3 annual measurement occasions (i.e., preschool, kindergarten, first grade). Supporting the first link in the hypothesized mediational chain, the results of structural equation modeling analyses indicated that caregiver intimate relationship instability uniquely predicted a pattern of response processes over a 1-year period characterized by negative family representations, dominant interpersonal strategies for regulating resources, and diminished task persistence. Latent difference score analyses of each of these response processes over the 1-year period, in turn, uniquely predicted a multiinformant (i.e., mother, teacher, experimenter) assessment of children's externalizing symptoms over a 2-year period. Mediational findings were robust after accounting for the negligible roles of residential and occupational changes as simultaneous predictors. Results are interpreted in the context of how they inform and support life history theory as well as other conceptual (e.g., attachment and emotional security theory) models. (PsycINFO Database Record (c) 2019 APA, all rights reserved).