Conventional knowledge tells us that mast cells are only important in the acute IgE-mediated reactions as seen in anaphylaxis, asthma and rhinitis. Yet, in recent years, much evidence has accumulated on the versatile role of mast cells in allergic inflammation. Here, we describe the novel and potential roles of mast cells in the late phase allergic reaction as well as in chronic allergic inflammation. Mast cells in patients with allergic rhinitis and asthma produce Th2 type cytokines, induce IgE synthesis in B cells and can autoactivate itself via the mast cell-IgE-FcepsilonRI cascade. In addition, mast cells upregulate the production of a variety of cytokines/chemokines in epithelial cells and fibroblasts and induce the recruitment of basophils, T cells and eosinophils into sites of allergic inflammation as well as their own intraepithelial accumulation. Furthermore, mast cells express MMPs and interact with extracellular matrix proteins and ASM and may play a role in nasal and bronchial hyperresponsiveness as well as tissue remodelling. In chronic rhinosinusitis with nasal polyps, the potential role of mast cells not only in orchestrating eosinophilic inflammation but also in the genesis and perpetuation of nasal polyp formation via FcepsilonRI and TLR mediated activation is also of growing interest.