As cells multiply in embryonic development they adopt different fates such as those of cells in our brain, muscles and blood. We now know that these cellular decisions are not so much based on which gene each cell expresses, but on when, where and how fast these genes are expressed. This regulation is mostly realized by molecules that bind to the DNA and activate or repress nearby genes. In this project, we will engage in a theory/experiment discourse aimed at reaching a predictive understanding of how the number, placement and affinity of these binding sites dictates cellular decision-making using the fruit fly embryo as a case study. Specifically, we will engage in theoretical modeling using equilibrium and non-equilibrium statistical mechanics, and test these predictions by imaging cellular decision-making in single cells of living fly embryos.