This latest Series on Maternal and Child Undernutrition Progress, includes three new papers that build upon findings from the previous 2008 and 2013 Series, which established an evidence-based global agenda for tackling undernutrition over the past decade. The papers conclude that despite modest progress in some areas, maternal and child undernutrition remains a major global health concern, particularly as recent gains may be offset by the COVID-19 pandemic. The Series reiterates that previously highlighted interventions continue to be effective at reducing stunting, micronutrient deficiencies, and child deaths and emphasizes the importance of delivering these nutrition interventions within the first 1,000 days of life. Multiple micronutrient supplementation (MMS) is highlighted as one of the key interventions to improve maternal nutrition.