Periostin (OSF-2) is secreted as a 91 kDa homodimeric soluble extracellular matrix protein expressed in collagen-rich fibrous connective tissues. There are at least 7 isoforms of Periostin, caused by alternative splicing (http://www.uniprot.org/uniprot/Q15063). Periostin is involved in osteoblast recruitment, attachment and spreading. It has been associated with the epithelial-mesenchymal transition in cancer and with the differentiation of mesenchyme in the developing heart. Periostin has functions in osteology, tissue repair, oncology, cardiovascular and respiratory diseases, and in various inflammatory settings.