Interleukin (IL)-33, a member of the IL-1 family of cytokines, is involved in innate and adaptive immune responses via interaction with its receptor, ST2. Activation of ST2 signalling by IL-33 triggers pleiotropic immune functions in multiple ST2-expressing immune cells, including macrophages, neutrophils, eosinophils, basophils, mast cells, type 2 helper T cells, regulatory T cells, and group 2 innate lymphoid cells. IL-33-mediated effector functions contribute to the tissue inflammatory and reparative responses in various organs including lung, skin, kidney, central nerve system, cardiovascular system, and gastrointestinal system. Endogenous IL-33/ ST2 signaling exhibits diverse immune regulatory functions during progression of different diseases. IL-33 likely functions as a disease sensitizer and plays pathological roles in inflamed tissues in allergic disorders that involve hyperreactive immune responses in the context of skin and pulmonary allergy. However, IL-33 also mediates tissue-protective functions during the recovery phase following tissue injury in the central nerve system and gastrointestinal system. Modulation of the IL-33/ST2 axis, therefore, represents a promising strategy for treating immune disorders that involve dysregulation of the cytokine signalling. In the past two decades, therapeutic strategies blocking IL-33/ST2 have been extensively studied for the treatment of diseases in animal models. In this review, the current progress on the development of therapeutic biologics for targeting IL-33/ST2 signalling in inflammatory diseases is summarized.