Violence and aggression represent a serious problem, with significant cost and impact at individual and societal level. There has been increasing interest in the potential of mindfulness interventions to decrease levels of violence and aggression. This paper systematically reviews the evidence to assess the effectiveness of mindfulness interventions for the reduction of violence and aggression levels. Five electronic databases were searched, and methods followed published guidance for systematic reviews. Studies that used a mindfulness intervention and measured outcomes of aggression and violence in adult populations were included. The Quality Assessment Tool for Quantitative Studies was utilised to evaluate the quality of included studies. Twenty-two studies met the eligibility criteria, including fourteen randomised studies, three non-randomised studies and five cohort studies. The interventions investigated included mindfulness, acceptance and commitment therapy, dialectical behaviour therapy and yoga with meditation. Overall, the results suggest that mindfulness-based interventions, with the possible exception of DBT, may be effective in reducing aggression and violence. They also suggest that mindfulness may relate to the processes of aggression through emotion regulation. However, papers were of variable quality, with weaknesses in both methodology and the reporting of data. Further good quality controlled studies with full and transparent reporting are needed to confirm these results, and to explore the elements of mindfulness which interact with mechanisms of aggression. • This review compiles all current evidence on the effectiveness of mindfulness-based interventions to decrease aggression and violence in adults • A detailed critique of the included studies is presented with the results categorised by type of mindfulness-based intervention • We observed heterogeneity in population, study design, intervention, methods and outcome measures used in the included studies • The results in 16 of the 22 studies suggest that mindfulness had an impact on violence and aggression, with effect sizes ranging from 0.21 to 0.87