The development of an embryo in its early stages involves a series of processes in which cells interact and organize to form tissues. In humans, these stages are studied with animal models, stem cells and cell aggregates that mimic natural development phases, or with human embryos, depending on their availability and a strict protocol. Now, in back-to-back papers published online in Nature, scientists from Yale University and the University of Cambridge have two new embryonic models formed from human stem cells to study development after embryo implantation in the uterus.