BACKGROUND: Contraception provides significant benefits for women's and children's health, yet many women have an unmet need for contraception. Rapid expansion in the use of mobile phones in recent years has had a dramatic impact on interpersonal communication. Within the health domain text messages and smartphone applications offer means of communication between clients and healthcare providers. This review focuses on interventions delivered by mobile phone and their effect on use of contraception. OBJECTIVES: To evaluate the benefits and harms of mobile phone-based interventions for improving contraception use. SEARCH METHODS: We used standard, extensive Cochrane search methods. The latest search date was August 2022. SELECTION CRITERIA: We included randomised controlled trials (RCTs) of mobile phone-based interventions to improve forms of contraception use amongst users or potential users of contraception. DATA COLLECTION AND ANALYSIS: We used standard Cochrane methods. Our primary outcomes were 1. uptake of contraception, 2. uptake of a specific method of contraception, 3. adherence to contraception method, 4. safe method switching, 5. discontinuation of contraception and 6. pregnancy or abortion. Our secondary outcomes were 7. road traffic accidents, 8. any physical or psychological effect reported and 9. violence or domestic abuse. MAIN RESULTS: Twenty-three RCTs (12,793 participants) from 11 countries met our inclusion criteria. Eleven studies were conducted in high-income resource settings and 12 were in low-income settings. Thirteen studies used unidirectional text messaging-based interventions, six studies used interactive text messaging, four used voice message-based interventions and two used mobile-phone apps to improve contraception use. All studies received funding from non-commercial bodies. Mobile phone-based interventions probably increase contraception use compared to the control (odds ratio (OR) 1.30, 95% confidence interval (CI) 1.06 to 1.60; 16 studies, 8972 participants; moderate-certainty evidence). There may be little or no difference in rates of unintended pregnancy with the use of mobile phone-based interventions compared to control (OR 0.82, 95% CI 0.48 to 1.38; 8 trials, 2947 participants; moderate-certainty evidence). Subgroup analysis assessing unidirectional mobile phone interventions versus interactive mobile phone interventions found evidence of a difference between the subgroups favouring interactive interventions (P = 0.003, I2 = 88.5%). Interactive interventions had an OR of 1.71 (95% CI 1.28 to 2.29; P = 0.0003, I2 = 63%; 8 trials, 3089 participants) whilst unidirectional interventions had an OR of 1.03 (95% CI 0.87 to 1.22; P = 0.72, I2 = 17%; 9 trials, 5883 participants). Subgroup analysis assessing high-income versus low-income trial settings found no difference between groups (subgroup difference test: P = 0.70, I2 = 0%). Only six trials reported on safety and unintended outcomes; one trial reported increased partner violence whilst another four trials reported no difference in physical violence rates between control and intervention groups. One trial reported no road traffic accidents with mobile phone intervention use. AUTHORS' CONCLUSIONS: This review demonstrates there is evidence to support the use of mobile phone-based interventions in improving the use of contraception, with moderate-certainty evidence. Interactive mobile phone interventions appear more effective than unidirectional methods. The cost-effectiveness, cost benefits, safety and long-term effects of these interventions remain unknown, as does the evidence of this approach to support contraception use among specific populations. Future research should investigate the effectiveness and safety of mobile phone-based interventions with better quality trials to help establish the effects of interventions delivered by mobile phone on contraception use. This review is limited by the quality of the studies due to flaws in methodology, bias or imprecision of results.