Eosinophils are the predominant inflammatory cells recruited to allergic airways. In this article, we show that human and murine eosinophils express SWAP-70, an intracellular RAC-binding signaling protein, and examine its role in mediating eosinophil trafficking and pulmonary recruitment in a murine model of allergic airway inflammation. Compared with wild-type eosinophils, SWAP-70-deficient (Swap-70 -/-) eosinophils revealed altered adhesive interactions within inflamed postcapillary venules under conditions of blood flow by intravital microscopy, exhibiting enhanced slow rolling but decreased firm adhesion. In static adhesion assays, Swap-70 -/- eosinophils adhered poorly to VCAM-1 and ICAM-1 and exhibited inefficient leading edge and uropod formation. Adherent Swap-70 -/- eosinophils failed to translocate RAC1 to leading edges and displayed aberrant cell surface localization/distribution of α4 and Mac-1. Chemokine-induced migration of Swap-70 -/- eosinophils was significantly decreased, correlating with reduced intracellular calcium levels, defective actin polymerization/ depolymerization, and altered cytoskeletal rearrangement. In vivo, recruitment of eosinophils to the lungs of allergen-challenged Swap-70 -/- mice, compared with wild-type mice, was significantly reduced, along with considerable attenuation of airway inflammation, indicated by diminished IL-5, IL-13, and TNF-α levels; reduced mucus secretion; and improved airway function. These findings suggest that regulation of eosinophil trafficking and migration by SWAP-70 is important for the development of eosinophilic inflammation after allergen exposure.