Routine immunizations and new vaccine introductions are two best buys in global health. But while immunization coverage has increased dramatically in the last decade, more must be done to ensure every child is reached. To bridge this gap, we need reliable, easily accessed and actionable data on the barriers impeding immunizations, coupled with trained data users at all levels of the health system. The BID Initiative is grounded in the belief that better data, plus better decisions will lead to better health outcomes. Partnering with Tanzania and Zambia, the BID Initiative developed, tested, and rolled out interventions that address some of the most pressing routine immunization service delivery challenges, such as poor visibility into vaccine supplies and difficulty identifying children who default on immunization schedules. These seven briefs summarize the BID Initiative’s approaches and interventions, and share recommendations and lessons learned for others interested in improving immunization data quality and use.