The remarkable capacity of mammalian embryos to self-organize is preserved in human pluripotent stem cells (hPSC), which on micropatterned surfaces form structures with reproducible spatial organization that resemble the early embryo. hPSCs therefore provide a powerful model to study the mechanisms of early human development. Secreted signaling molecules play a key role in orchestrating development, but a quantitative understanding of how they do this is lacking. According to current paradigm, it is the level of signaling that determines a cell’s response, but this model fails to correctly predict cell fate decisions. Two shortcomings may explain this. First, the model is static, ignoring the essential role of time. Second, different signals have typically been studied separately, despite the fact that they act in a fundamentally combinatorial manner. To address this, my lab has developed methods to track signaling in hPSCs over time and to measure many signals at once in snapshots. I will discuss how we are applying these methods to build a quantitative understanding of how cell signaling controls cell fate decisions.