The present invention provides interleukin-33 (IL-33) antagonists comprising one or more IL-33-binding domains and one or more multimerizing domains and methods of using the same. According to certain embodiments of the invention, the IL-33-binding domains can comprise an IL-33-binding portion of an ST2 protein and/or an extracellular portion of an IL-1RAcP protein. The IL-33 antagonists of the invention are useful for the treatment of diseases and disorders associated with IL-33 signaling and/or IL-33 cellular expression, such as infectious diseases, inflammatory diseases, allergic diseases and fibrotic diseases.