A narrative systematic review was conducted to describe the available evidence from physical activity (PA) interventions that targeted girls aged 5–18 years and to determine their effectiveness and key characteristics of success. Systematic literature searches were conducted using four databases: PubMed, Web of Science, PsychInfo and SPORTDiscus and by examining the reference lists of included articles and published relevant reviews, to identify studies published in English from 2000 to July 2010. Randomized controlled trials or quasi-experimental designs with pre-test and post-test behavioral outcome data (objective or self-report measure) were included. Methodological quality was assessed using a checklist and conclusions were made concerning effectiveness. A total of 29 articles were reviewed, describing the evaluation of 21 interventions. Ten studies reported a favorable intervention effect upon PA outcomes, seven of which were rated as having a high methodological quality. Multi-component school-based interventions that also offer a physical education that address the unique needs of girls seemed to be the most effective. Although family support is revealed as ineffective, peer strategies showed promising evidence. The review finishes highlighting possible intervention strategies and reporting areas where further investigation is required.