Hybridization often inhibits speciation by causing gene flow between incipient species before the completion of speciation. At the same time, however, there is growing evidence that hybridization often creates novel phenotypes by mixing genomes of different species and that this mechanism can promote rapid speciation and adaptive radiation. However, there is still no systematic understanding of the conditions under which hybridization inhibits and promotes species diversification. In this presentation, I first provide an overview of existing theories on the roles of hybridization in speciation processes including my own works. Then, I introduce my recent study offering a new mechanism of hybrid speciation. In this study, I developed simulation models considering evolution of mating traits (e.g., mating season, genitalia shapes, sexual displays) in a hybrid zone. Simulations showed that recurrent hybridization in a hybrid zone drives stochastic phenotypic evolution of mating traits. Under certain conditions, the hybridization-driven stochastic evolution almost certainly led to speciation because it continued endlessly until the hybrid population evolved a novel mating trait phenotype that reproductively isolated it from parental lineages. These results suggest that the evolutionary dynamics unique to hybrid zones can drive speciation even without adaptive advantage for hybrids.