Over the past few years, epidermal growth factor receptor has emerged as one of the most important targets in tumorgenesis and several drugs targeting signal transduction pathways have been developed. The first among these agents to be approved for the treatment of NSCLC was gefitinib, a potent, selective and reversible inhibitor of HER1/EGFR tyrosine kinase activity. The review summarizes its clinical development and the new therapeutic options, with particular focus on predictive markers of susceptibility to this drug.