Our understanding of early human embryonic development is hampered by the lack of suitable models. In this week’s issue, two papers seek to address this problem in the form of lab-grown cellular models of the human blastocyst — the ball of cells that forms within the first few days of embryo development. The two teams used different starting points: in one article, Jun Wu and his co-workers used human pluripotent cells, in the other, Jose Polo and his colleagues used adult fibroblasts undergoing reprogramming. Both groups were able to induce their respective cells to self-organize in a dish to form three-dimensional structures that resemble blastocysts. Both types of structure — named blastoids by Wu et al. and iBlastoids by Polo et al. — represent an integrated model of the early human embryo, although the teams note that their structures are not equivalent to human blastocysts. Nevertheless, the researchers believe that blastoids and iBlastoids will prove valuable in studies of infertility and pregnancy loss.