Tumor metastasis is a multistep pathological process involved in the final phase of tumor development. During this process, epithelium-derived tumor cells undergo fibroblast-like transformation, referred to as epithelial-mesenchymal transition (EMT), which contributes to aggressive behavior of tumors. We identify periostin, a mesenchyme-specific gene product, as a contributor to EMT and metastatic potential. Stable expression of a periostin transgene in tumorigenic but non-metastatic 293T cells caused cells to undergo fibroblast-like transformation accompanied by increased expressions of vimentin, epidermal growth factor receptor (EGFR), and matrix metalloproteinase-9. The cells expressing ectopic periostin increased cell migration, invasion, and adhesion by 2-9-fold. Invasive characteristics required signaling through integrin alpha(v)beta5 and EGFR. In addition, periostin-engineered 293T cells formed metastases in immunodeficient mice following either cardiac inoculation or injection into mammary fat pad. These data demonstrate an active role for periostin in EMT and metastasis that requires cross-talk between integrin and EGFR signaling pathways.