Left-sided expression ofNodalin the lateral plate mesoderm is a conserved feature necessary for the establishment of normal left–right asymmetry during vertebrate embryogenesis. By using gain- and loss-of-function experiments in zebrafish and mouse, we show that the activity of the Notch pathway is necessary and sufficient forNodalexpression around the node, and for proper left–right determination. We identify Notch-responsive elements in theNodalpromoter, and unveil a direct relationship between Notch activity andNodalexpression around the node. Our findings provide evidence for a mechanism involving Notch activity that translates an initial symmetry-breaking event into asymmetric gene expression.