Importance: In 2021, the American Academy of Pediatrics published a policy statement seeking to create a paradigm shift away from a focus on childhood toxic stress and toward the emphasis on early relational health (ERH) as a buffer for childhood adversity and promoter of life-course resilience. A comprehensive appraisal of the efficacy of contemporary parent/caregiver-child interventions in — primarily — improving ERH, and — secondarily — enhancing child wellbeing and neurodevelopment is needed to guide widespread implementation and policy. Objective: Determine the effectiveness of contemporary early dyadic parent/caregiver-infant interventions on ERH, child socio-emotional functioning and development, and parent/caregiver mental health. Data Sources: PubMed, Medline, Cinhal, ERIC, and PsycInfo were searched on April 28, 2022. Additional sources: clinical trial registries (clinicaltrials.gov, ISRCTN Registry, EU Clinical Trials Register, Australian New Zealand Clinical Trials Registry), contacting authors of unpublished/ongoing studies, backward/forward reference-searching. Study Selection: Studies targeting parent/caregiver-infant dyads and evaluating effectiveness of a dyadic intervention were eligible. Study selection was performed in duplicate, using Covidence. Data Extraction and Synthesis: Cochrane methodological guidance presented per PRISMA guidelines. Data extraction and risk of bias assessment were completed in duplicate with consensuses by first author. Data were pooled using inverse-variance random effects models. Main Outcomes and Measures: The primary outcome domain was ERH. Secondary outcome domains were child socio-emotional functioning and development, and parent/caregiver mental health, and were only considered in studies where at least one ERH outcome was also measured. The association between dose of intervention and effect estimates was explored. Results: 93 studies (14,993 parent/caregiver-infant dyads) met inclusion criteria. Based on very low to moderate quality of evidence, we found significant non-dose-dependent intervention effects on several measures of ERH, including bonding, parent/caregiver sensitivity, attachment, and dyadic interactions, and a significant effect on parent/caregiver anxiety, but no significant effects on other child outcomes. Conclusion: Current evidence does not support the notion that promoting ERH through early dyadic interventions ensures optimal child development, despite effectively promoting ERH outcomes. Given the lack of an association with dose of intervention, the field is ripe for novel, innovative, cost-effective, potent ERH intervention strategies that effectively and equitably improve meaningful long-term child outcomes.