This Campbell systematic review examines the predictors of youth gang membership in low‐ and middle‐income countries. The review summarises findings from eight reports from five countries and the Caribbean region. The lack of available evidence limits the extent to which clear conclusions can be drawn about the factors associated with youth gang membership. The review is based on a very small number of studies, and has significant limitations in coverage. The limited evidence of the correlates of youth gang membership suggests factors that may drive gang membership and suggests areas where interventions may prove promising in the family, school, and community domains, as well as provide a starting point for future studies. Plain language summary Evidence shows which factors predict gang membership in low‐ and middle‐income countries, but more studies needed Youth gang membership is associated with delinquency, violent crime and trafficking. A range of individual, peer, family, school and community factors can predict the likelihood of youths getting involved with gangs. Knowledge of these factors can be helpful for reducing gang membership. What is this review about? Youth gang membership is associated with delinquency, violent crime and trafficking – and gang members are themselves frequently the victims of these offences. Yet youth gangs can also provide a form of social capital, a sense of belonging and purpose to disenfranchised youth. This review identifies the factors associated with young people joining gangs, and the differences between gang‐involved and non‐gang‐involved youth. Understanding these associations is essential to reduce the levels of gang membership and the incidence of related violence. What is the aim of this review? This Campbell systematic review examines the predictors of youth gang membership in low‐ and middle‐income countries. The review summarises findings from eight reports from five countries and the Caribbean region. What studies are included? Studies of youth gangs in in low‐ and middle‐income countries were included, with participants aged 10‐29 years. The studies had to assess an individual predictor or correlate of youth gang membership, where the predictor or correlate is a single characteristic, not a conglomeration of multiple constructs. Included studies had designs including data on both gang‐involved and non‐gang‐involved youth, recruited with strategies that were eligible. Nine studies met the eligibility criteria and were included in the review. One of these studies did not report all the required data and so was not included in the analyses. The studies were conducted in Turkey, Trinidad and Tobago, the Caribbean, El Salvador, China and Brazil. Factors associated with gang membership Domain Significantly associated with gang membership No significant association with gang membership Individual Delinquency Alcohol and soft drug use Male gender Risky sexual behaviours Employment Psychological risk factors (low self‐control, impulsivity) and lack of psychological protective factors (empathy, future orientation, belief in moral order) Victimisation Age Minority ethnicity Protective behaviours surrounding sexual behaviour or alcohol and soft drug use. Peer Socialising with delinquent peers Socialising with pro‐social peers Family Negative family environments Lack of parental monitoring Middle‐income families had greater odds of reporting youth gang membership than those from either high or low‐income families (finding from one study) Parental education Parental attitudes to antisocial behaviour School Low school attachment Exposure to violence at school Educational difficulties Opportunities for prosocial involvement Level of education School type School performance Community Exposed to neighbourhood violence Neighbourhood environment risk or protective factors, or geography What are the main results in this review? The eight studies analysed in the review address the associations between life events and circumstances, and the likelihood of being a youth gang member across five domains: individual, peers, family, school and community. Significant associations were found with factors in each domain. What do the findings of this review mean? The lack of available evidence limits the extent to which clear conclusions can be drawn about the factors associated with youth gang membership. The review is based on a very small number of studies, and has significant limitations in coverage. The limited evidence of the correlates of youth gang membership suggests factors that may drive gang membership and suggests areas where interventions may prove promising in the family, school, and community domains, as well as provide a starting point for future studies. How up‐to‐date is this review? The review authors searched for studies published up to September 2013. This Campbell systematic review was published in December 2018. Summary Background Youth gang membership is well documented throughout low‐ and middle‐income countries, and youth gang members are increasingly associated with delinquency, violent crime and trafficking. They are also frequently the victims of these offences, often in disproportionate numbers compared to non‐gang youth. Yet youth gangs can also provide a form of social capital, a sense of belonging and purpose to disenfranchised youth. Extensive research, primarily from high‐income countries, has categorized five domains of risk and protective factors for youth gang involvement, drawn from the realm of developmental psychology. These domains are: Individual, Peer, Family, School, and Community. Youth gang membership is seen as the culmination of interrelated structural and process factors, which in combination with negative life events may increase the attractiveness of gang membership. This review aimed to identify the factors associated with young people joining gangs, and to identify and quantify the differences between gang‐involved and non‐gang‐involved youth. Understanding these associations is essential to reduce the levels of gang membership and the incidence of related violence. Objectives This review addresses two key objectives: (1) to synthesize the published and unpublished empirical evidence on the factors associated with membership of youth gangs in low‐ and middle‐income countries;(2) to assess the relative strength of the different factors across the domains of individual, family, school, peer group and community. Search methods The search was conducted in English, French, Chinese, Arabic, Russian, Spanish and Portuguese. We searched 55 locations including academic databases, journals, and grey literature locations, and located over 54,000 documents to screen. Selection criteria We included studies meeting the following criteria: Reports on youth gangs All participants aged 10‐29 years Located in low‐ or middle‐income country Assesses an individual predictor or correlate of youth gang membership Predictor or correlate is a single characteristic Predictor or correlate is not a conglomeration of multiple constructs Eligible recruitment strategy for respondents Study design included data on both gang involved and non‐gang involved youth. Data collection and analysis We conducted a broad abstract screening of over 54,000 titles and abstracts, followed by a close abstract screening of 1509 abstracts. We screened the full‐text of 98 documents. Nine studies met the eligibility criteria and were included in the review. One of these studies did not report sufficient data to allow the calculation of a standardized effect size, and so was not included in the analyses. A total of 85 independent effect sizes were extracted from the eight studies with sufficient data to create a standardized effect size. We calculated Cohen's d from continuous data and the Log Odds Ratio from dichotomous data. All effects were categorized into the five predictor domains, and further classified into conceptually similar group and risk or protective factors. We synthesized the data using multiple random effects meta‐analyses with inverse variance weighting. Results The eight studies analysed in the review address the associations between life events and circumstances, and the likelihood of being a youth gang member. All studies were based on cross‐sectional survey data, using different statistical methods to identify correlations between youth characteristics and the likelihood of being a member of a youth gang. No longitudinal, prospective or retrospective studies were located. The studies were conducted in Turkey, Trinidad and Tobago, the Caribbean, El Salvador, China and Brazil. We organized the analyses according to five domains of factors that may be associated with youth gang involvement and summarize the main findings below: Individual factors Delinquency, alcohol and soft drug use, male gender, risky sexual behaviours, employment, psychological risk factors (low self‐control, impulsivity), and victimisation were each associated with significantly higher odds of youth gang membership. Psychological protective factors (empathy, future orientation, belief in moral order) were associated with lower odds. No association between youth gang membership and age, minority ethnicity, or protective behaviours surrounding sexual behaviour or alcohol and soft drug use. Peer factors There is a small amount of evidence that socialising with delinquent peers is associated with increased odds of youth gang membership, but there is no significant relationship demonstrated between socialising with pro‐social peers and youth gang membership. Family factors Negative family environments are associated with more youth gang membership, while both a positive family environment and parental monitoring were associated with lower odds. One study showed that youth from middle‐income families had greater odds of reporting youth gang membership than those from either high or low‐income families. No significant relationship was seen between youth gang membership and parental education or parental attitudes to antisocial behaviour. School factors Low school attachment, exposure to violence at school, educational difficulties and opportunities for prosocial involvement all show significant association with more youth gang membership. No significant relationship was seen between youth gang membership and level of education, school type, or school performance. Community factors There were significantly higher odds of youth gang membership amongst those who reported that they were exposed to violence in their neighbourhood. No demonstrated association between youth gang membership and neighbourhood environment risk or protective factors, or geography. Gang membership is typically viewed as a culmination of interrelated structural and process factors. Understanding the factors associated with youth gang membership can help inform prevention strategies to reduce the levels of youth gang membership and the incidence of youth gang violence. Unfortunately the small number of studies contributing to any analysis limits the conclusions that can be drawn from this study. Moreover, many of the individual and peer associations identified in this review (such as delinquency, drug use, and sexual risk factors) may be as a result of gang membership rather than its cause. However, our results suggest certain family, school, and community level factors associated with gang membership that could be addressed through targeted preventive interventions, particularly family environment, parental monitoring, school attachment, educational difficulties, and exposure to violence in the home, at school, or in the community. Authors’ conclusions The lack of available evidence limits the extent to which we can draw any clear conclusions about the factors associated with youth gang membership. This current review is based on a very small number of studies, and has significant limitations in coverage; however it provides some limited evidence of the correlates of youth gang membership. Specifically, this review suggests factors that may drive gang membership and suggests areas where interventions may prove promising in the family, school, and community domains, as well as provide a starting point for future studies.