Our understanding of lineage decisions in early human development has been greatly aided by embryonic stem cell lines, which avoid many of the practical and ethical difficulties of in vivo material. A new paper in Development exploits naive human embryonic stem cells to generate in vitro models for the extra-embryonic endoderm. We caught up with first authors Madeleine Linneberg-Agerholm and Yan Fung Wong, and their supervisor Josh Brickman, Professor of Stem Cell and Developmental Biology at the Novo Nordisk Foundation Center for Stem Cell Biology (DanStem) in Copenhagen, to hear more about the work.