In June 2019, BMJ Global Health published a supplement with six papers by the Countdown to 2030 to address the challenges in measurement and monitoring of reproductive, maternal, newborn and child health and nutrition (RMNCH&N) in the context of the sustainable development goals. The six-paper series seeks to advance the measurement and monitoring of effective coverage of RMNCH&N interventions, inequalities in the RMNCH&N continuum of care, drivers of RMNCH&N especially governance, early childhood development, nutrition intervention coverage, and RMNCH&N in conflict settings. This includes the introduction of new and improved measurement frameworks and measurement methods, as well as critical assessments of evidence based on current measurement approaches.