Cilia play an essential role in left-right (L-R) symmetry breaking in many of vertebrates including the fish, frog and mouse. In the mouse embryo, for instance, rotational movement of motile cilia at the node generates leftward fluid flow, which is sensed by immotile cilia located at the periphery of the node. I will discuss 1) how motile cilia are correctly formed at the node and generate the unidirectional flow, 2) how the flow is sensed by immotile cilia, possible involvement of ciliary Ca2+ in flow sensing, 3) how the fluid flow leads to degradation of Cerl2/Dand5 mRNA, the readout of flow-induced signal. On the other hand, other animals such as chick do not required cilia for L-R symmetry breaking. I will discuss L-R symmetry breaking in reptiles: whether cilia are involved or not, and how key genes such as Nodal, Lefty and Cerl are expressed and regulated in reptile embryos. At the end, I will speculate evolutionary conservation of the symmetry-breaking mechanism among vertebrates.