Plants have developed sophisticated defense systems during their long-time interaction with insects. About three decades ago, it was found that insect-damaged plants can prime their neighbors to express defense proteins, and this phenomenon was called “plant-plant communication”. A series of studies have focused on this topic since then. Results indicate that green-leaf volatiles and terpenes are the main chemicals emitted from the infested plant to the healthy neighbor plants, while direct and indirect defenses of the neighbors may both be regulated. An important consensus about plant-plant communication mechanisms until now is that the volatile organic chemicals do not induce resistance directly, but sensitize the receiver plant for augmented response to subsequent damages, which is called “priming”. However, the molecular mechanism of this phenomenon is unclear. We used Arabidopsis thaliana genome arrays and mutants to examine the molecular mechanisms of plant-plant communication. Our results indicate that several volatiles are effective signals, and the active volatiles are correlated with their emission rhythms to achieve the optimum effect. The ethylene pathway is indispensable for sensing the induction signal in the early phase of induction, while Jasmonic acid signal can amplify the effects. As the mechanisms of plant-plant communication become clearer, future research may focus on the origin and evolution of this phenomenon.