Churg-Strauss syndrome is a rare, small-sized vessel systemic necrotizing vasculitis that was first described in the early 1950s. Its most typical presentation consists of the appearance, in a patient with late-onset asthma, of vasculitic manifestations, like fever, cutaneous purpura and mononeuritis multiplex. In such a setting, the combination of blood eosinophilia and inflammatory syndrome is highly suggestive of the diagnosis, which can be further supported by the detection of antineutrophil cytoplasmic autoantibodies (ANCN), especially P-ANCA with anti-myeloperoxidase specificity, in almost 40% of the patients, and the presence of eosinophilic granulomas and/or necrotizing vasculitis in an affected-tissue biopsy. Although these disease hallmarks are now well-known, its pathophysiological mechanisms remain to be fully understood. Several gene polymorphisms and immune dysregulations are surely implicated, ranging from direct eosinophil toxicity to T- or even B-cell dysfunctions and, altogether, suggesting the existence of different disease stages and subsets according to the predominantly involved pathway. Only half the patients initially have severe life-threatening manifestations, like cardiac involvement, which require prompt aggressive treatments based on combined corticosteroids and immunosuppressants (mainly cyclophosphamide). Other less severe disease forms can usually be controlled with corticosteroids alone. Even though this current standardized therapy quite effectively and safely obtains remission, more than three-quarters of all the patients will remain corticosteroid-dependent, mostly because of residual asthma and/or eosinophilia. Hence, progress is needed in Churg-Strauss syndrome's therapeutic management, and better understanding of the complex disease mechanisms may aid such a quest.