Not yet reviewed by Pith; the record is open.

Recent 3D organ reconstitution studies show that a group of stem cells can establish a body axis and acquire different fates in a spatially organized manner. How such symmetry breaking happens in the absence of external spatial cues, and how developmental circuits are built to permit this is largely unknown. Here, we review spontaneous symmetry breaking phenomena in organoids, and hypothesize underlying patterning mechanisms that involve interacting diffusible species. Recent theoretical advances offer new directions beyond the prototypical Turing model. Experiments guided by theory will allow us to predict and control organoid self-organization.