Genetic engineering is an important tool for introducing desired genes into poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch). We describe in this chapter an Agrobacterium tumefaciens-mediated transformation protocol for poinsettia. A detailed description of genetic transformation, antibiotic selection, subsequent regeneration via somatic embryogenesis, and rooting as well as molecular and morphological analyses is included. The methodology described here could facilitate the future engineering of poinsettia for research purpose as well as commercial production of poinsettia plants with improved resistance or novel traits.