The National Academies of Sciences, Engineering, and Medicine last reviewed the state of the science on nutrition during pregnancy and lactation 30 years ago. The resulting consensus study reports from the Institute of Medicine--Nutrition During Pregnancy (IOM, 1990) and Nutrition During Lactation (IOM, 1991)--summarized the scientific evidence and provided nutrient recommendations. In the decades since the release of these two reports, the body of evidence on the relationships between nutrition during pregnancy and lactation and maternal and infant health and chronic disease has continued to grow and evolve. At the same time, the demographics of the population have shifted, giving rise to new considerations. To explore the evidence that has emerged, the National Academies conducted a 2-day workshop in January 2020. This publication summarizes the presentations and discussions from the workshop.