Asthma is a complex inflammatory disease of the lung characterized by variable airflow obstruction, bronchial hyperresponsiveness, and airway inflammation. Inflammation in asthma consists of airway infiltration by mast cells, lymphocytes, and eosinophils. There is accumulating evidence that CD4+ lymphocytes with a Th2-cytokine pattern play a pivotal role in the pathogenesis of asthma. These cells orchestrate the recruitment and activation of the primary effector cells of the allergic response (mast cells and eosinophils), through the release of cytokines such as IL-4, IL-5, and IL-13. Allergic inflammation is also implicated in airway epithelium changes, although the mechanisms by which inflammatory cells and, in particular, T cells interact with the epithelium are not completely clarified. This paper explores the role of T cells in the allergic inflammation of asthma.