Purpose: Illness uncertainty pervades individuals' experiences of cancer across the illness trajectory and is associated with poor psychological adjustment. This review systematically examined the characteristics and outcomes of interventions promoting illness uncertainty management among cancer patients and/or their family caregivers. Methods: PubMed, Scopus, PsycINFO, Cumulative Index to Nursing and Allied Health Literature (CINAHL), Embase, and Cochrane Database of Systematic Reviews were systematically searched for relevant literature. We included randomized controlled trials (RCTs) and quasi-experimental studies focusing on interventions for uncertainty management in cancer patients and/or their family caregivers. Results: Our database searches yielded 26 studies. Twenty interventions were only offered to cancer patients, who were mostly elder, female, and White. All interventions included informational support. Other intervention components included emotional support, appraisal support, and instrumental support. Most interventions were delivered in person and via telephone (n = 8) or exclusively in person (n = 7). Overall, 18 studies identified positive intervention effects on illness uncertainty outcomes. Conclusion: This systematic review foregrounds the promising potential of several interventions—and especially multi-component interventions—to promote uncertainty management among cancer patients and their family caregivers. To further improve these interventions' effectiveness and expand their potential impact, future uncertainty management interventions should be tested among more diverse populations using rigorous methodologies.