The aim of this article was to systematically review the quality and efficacy of the current evidence for mindfulness-based interventions (MBIs) in patients with mild cognitive impairment (MCI), patients with dementia (PwD), and their caregivers. We identified 20 randomized controlled trials (RCTs) (11 for patients, 9 for caregivers) published in the last 15 years. Evidence suggested that MBIs are highly acceptable and credible treatments for patients with MCI, PwD and caregivers. Specifically, for PwD, the results indicated that the magnitude of post-treatment effects of MBIs are in the medium to large range for psychosocial outcomes, and in the small to medium range for cognitive functioning; however, treatment effects on dementia biomarkers were mixed, ranging from small to large, depending on the outcome measure. Findings also evidenced salutary effects of MBIs for caregivers of PwD, with post-treatment effects ranging from medium to large for caregiver stress and burden and large effects for quality of life, and mixed outcomes for cognitive functioning, with effects in the small to large range. However, confidence in these findings is relatively limited due to methodological limitations, especially in terms of poor consistency in intervention strategies, outcome measures, and other key criteria across studies. To better assess the value of MBIs for these populations and optimize treatment outcomes, we recommend further research with improved study methodology (e.g., multi-method assessment, universal criterion and outcome measures, use of active control groups, larger sample sizes, long-term follow-up) to replicate current findings and enhance our understanding of underlying treatment mechanisms of MBIs.