Background: Immunization rates for children and adults are rising, but coverage levels have not reached optimal goals. As a result, vaccine-preventable diseases still occur. In an era of increasing complexity of immunization schedules, rising expectations about the performance of primary care, and large demands on primary care providers, it is important to understand and promote interventions that work in primary care settings to increase immunization coverage. One common theme across immunization programs in many nations involves the challenge of implementing a population-based approach and identifying all eligible recipients, for example the children who should receive the measles vaccine. However, this issue is gradually being addressed through the availability of immunization registries and electronic health records. A second common theme is identifying the best strategies to promote high vaccination rates. Three types of strategies have been studied: (1) patient-oriented interventions, such as patient reminder or recall, (2) provider interventions, and (3) system interventions, such as school laws. One of the most prominent intervention strategies, and perhaps best studied, involves patient reminder or recall systems. This is an update of a previously published review. Objectives: To evaluate and compare the effectiveness of various types of patient reminder and recall interventions to improve receipt of immunizations. Search methods: We searched CENTRAL, MEDLINE, Embase and CINAHL to January 2017. We also searched grey literature and trial registers to January 2017. Selection criteria: We included randomized trials, controlled before and after studies, and interrupted time series evaluating immunization-focused patient reminder or recall interventions in children, adolescents, and adults who receive immunizations in any setting. We included no-intervention control groups, standard practice activities that did not include immunization patient reminder or recall, media-based activities aimed at promoting immunizations, or simple practice-based awareness campaigns. We included receipt of any immunizations as eligible outcome measures, excluding special travel immunizations. We excluded patients who were hospitalized for the duration of the study period. Data collection and analysis: We used the standard methodological procedures expected by Cochrane and the Cochrane Effective Practice and Organisation of Care (EPOC) Group. We present results for individual studies as relative rates using risk ratios, and risk differences for randomized trials, and as absolute changes in percentage points for controlled before-after studies. We present pooled results for randomized trials using the random-effects model. Main results: The 75 included studies involved child, adolescent, and adult participants in outpatient, community-based, primary care, and other settings in 10 countries. Patient reminder or recall interventions, including telephone and autodialer calls, letters, postcards, text messages, combination of mail or telephone, or a combination of patient reminder or recall with outreach, probably improve the proportion of participants who receive immunization (risk ratio (RR) of 1.28, 95% confidence interval (CI) 1.23 to 1.35; risk difference of 8%) based on moderate certainty evidence from 55 studies with 138,625 participants. Three types of single-method reminders improve receipt of immunizations based on high certainty evidence: the use of postcards (RR 1.18, 95% CI 1.08 to 1.30; eight studies; 27,734 participants), text messages (RR 1.29, 95% CI 1.15 to 1.44; six studies; 7772 participants), and autodialer (RR 1.17, 95% CI 1.03 to 1.32; five studies; 11,947 participants). Two types of single-method reminders probably improve receipt of immunizations based on moderate certainty evidence: the use of telephone calls (RR 1.75, 95% CI 1.20 to 2.54; seven studies; 9120 participants) and letters to patients (RR 1.29, 95% CI 1.21 to 1.38; 27 studies; 81,100 participants). Based on high certainty evidence, reminders improve receipt of immunizations for childhood (RR 1.22, 95% CI 1.15 to 1.29; risk difference of 8%; 23 studies; 31,099 participants) and adolescent vaccinations (RR 1.29, 95% CI 1.17 to 1.42; risk difference of 7%; 10 studies; 30,868 participants). Reminders probably improve receipt of vaccinations for childhood influenza (RR 1.51, 95% CI 1.14 to 1.99; risk difference of 22%; five studies; 9265 participants) and adult influenza (RR 1.29, 95% CI 1.17 to 1.43; risk difference of 9%; 15 studies; 59,328 participants) based on moderate certainty evidence. They may improve receipt of vaccinations for adult pneumococcus, tetanus, hepatitis B, and other non-influenza vaccinations based on low certainty evidence although the confidence interval includes no effect of these interventions (RR 2.08, 95% CI 0.91 to 4.78; four studies; 8065 participants). Authors' conclusions: Patient reminder and recall systems, in primary care settings, are likely to be effective at improving the proportion of the target population who receive immunizations.