How an egg turns into an organism continues to baffle the imagination. We can describe how it happens and many of the particulars, but still struggle to comprehend how events at the levels of genes and cells produce a fruit fly, a sea urchin, or a baby. The fertilized egg, at bottom a single cell, undergoes multiple cycles of division with concurrent differentiation and transformations of shape, resulting in a multicellular embryo whose several regions are committed to develop into distinct organs. Differentiation relies on elaborate networks of control on gene expression that promote certain genes and silence others. Spatial organization of the embryo commonly involves diffusible “morphogens,” hormone-like substances that instruct cells as to their developmental fate. Chemical gradients are supplemented by diverse processes that draw on active transport, mechanical forces, and cell migration. Genes do not hold a comprehensive blueprint for development. They operate in the context of cells that are directed by both genes and self-organization, and there is no plan separable from its execution. How an egg turns into an organism may no longer be mysterious or miraculous, but it remains as wondrous as ever that an assemblage of lifeless molecules can build a butterfly.