INTRODUCTION: Access to antiretroviral treatment (ART) has substantially improved over the past decade. In this new era of HIV as a chronic disease, the continued success of ART will depend critically on sustained high ART adherence. The objective of this review was to systematically review interventions that can improve adherence to ART, including individual-level interventions and changes to the structure of ART delivery, to inform the evidence base for the 2013 WHO consolidated antiretroviral guidelines. DESIGN: A rapid systematic review. METHODS: We conducted a rapid systematic review of the global evidence on interventions to improve adherence to ART, utilizing pre-existing systematic reviews to identify relevant research evidence complemented by screening of databases for articles published over the past 2 years on evidence from randomized controlled trials (RCTs). We searched five databases for both systematic reviews and primary RCT studies (Cochrane Library, EMBASE, MEDLINE, Web of Science, and WHO Global Health Library); we additionally searched ClinicalTrials.gov for RCT studies. We examined intervention effectiveness by different study characteristics, in particular, the specific populations who received the intervention. RESULTS: A total of 124 studies met our selection criteria. Eighty-six studies were RCTs. More than 20 studies have tested the effectiveness of each of the following interventions, either singly or in combination with other interventions: cognitive-behavioural interventions, education, treatment supporters, directly observed therapy, and active adherence reminder devices (such as mobile phone text messages). Although there is strong evidence that all five of these interventions can significantly increase ART adherence in some settings, each intervention has also been found not to produce significant effects in several studies. Almost half (55) of the 124 studies investigated the effectiveness of combination interventions. Combination interventions tended to have effects that were similar to those of single interventions. The evidence base on interventions in key populations was weak, with the exception of interventions for people who inject drugs. CONCLUSION: Tested and effective adherence-enhancing interventions should be increasingly moved into implementation in routine programme and care settings, accompanied by rigorous evaluation of implementation impact and performance. Major evidence gaps on adherence-enhancing interventions remain, in particular, on the cost-effectiveness of interventions in different settings, long-term effectiveness, and effectiveness of interventions in specific populations, such as pregnant and breastfeeding women.