Neural crest cells migrate rapidly over long distances during early embryonic development of vertebrates, and their migration has been much studied as a model for chemotaxis and cancer metastasis. A curious observation is the "group advantage": in a chemokine gradient too shallow to induce a single cell to chemotax, a cluster of cells can demonstrate robust chemotaxis up the gradient. In this talk, I will describe a model that explains this behavior based on cell-cell interaction. Through contact inhibition and co-attraction, the cells modulate each other's Rac1 and RhoA dynamics on their membranes and achieve a common polarity. This affords a group of cells much stronger persistence in their chemotaxis than a single cell against ambient noise.