Genetic transformation technology of plants is one of the most powerful tools for cultivar improvement as well as for studying gene function in plants. In the past two decades, genetic transformation procedures for most of the commercially important orchids have been established. In our laboratory, we have concentrated our efforts to develop the genetic transformation methods for various ornamental plants, especially for commercially important orchids such as Phalaenopsis, Cymbidium, Dendrobium and Cattleya. Furthermore, we generated a series of transgenic plants in these orchid genera, which harbor the useful genes for disease and stress resistances, flower color, flower shape, plant height, etc. This review describes the summarized results of these orchid studies and some related topics on other horticultural plants.