Routine Immunization, though a cornerstone to population health, is continually bedeviled with lack of continuity among clients who already accessed services. In Nigeria, this has resulted in quite some set back in the EPI performance. Many methods have been attempted to address this issue of client dropout in the past - especially the traditional home visits which are even recommended by the leading heath organisations, but there has not been much success in sustaining client utilization of services. Real world best practices need to be applied to this contemporary problem for a sustainable solution to be reached. This book shows the methods and outcome of a study on the use of an SMS-based reminder-recall system for improvement of routine immunization performance.