Regulating when and where genes are expressed is essential to the proper development and health of all life. The remarkably robust nature of this regulation is illustrated during embryonic development where individual cells make decisions to lay out the future body plan of an animal. Mustafa Mir and his lab develop and apply new microscopes to directly visualize the molecular scale events that underlie gene expression within live embryos. By interrogating these events in their native contexts, the Mir lab aims to build a quantitative understanding of how gene expression is regulated and new approaches to correct it when it goes awry.