Eosinophils (Eos) are prominent inflammatory cells found in the sputum, airways, and airway walls during and after exacerbations of allergic asthma. These cells are potent secretors of a wide array of cytotoxic granule proteins, cytokines, and lipid mediators involved in the initiation and maintenance of the Th2-type inflammatory reaction. Even though respiratory viral and bacterial infections are known risk factors contributing to severity and prognosis, the induction of anti-microbial Th1 type responses can offset allergic Th2 responses. Emerging evidence suggests that the prolyl isomerase Pin1 plays important roles in both Th1 and Th2 immunity in the lung and especially during allergic disease. In this review, we summarize recent findings related to the role of Pin1 in the regulation of Eos differentiation, survival, migration, cytokine expression, and antiviral immunity in asthma.