Sensitivity to Her2-directed therapies is complex and involves expression not only of Her2 but also of other epidermal growth factor receptor (EGFR) family members, their ligands, and molecules that influence pathway activity, such as insulin-like growth factor-1 receptor, PTEN, and p27. The EGFR experience has taught us that responses can easily be diluted in an unselected cohort of patients. To date, trials of Her2-targeted therapies, such as trastuzumab, have been insufficiently powered to determine whether patients with non–small cell lung cancer (NSCLC) with Her2 gene amplification (rather than overexpression by immunohistochemistry) may benefit from these agents. It is unclear whether agents targeting Her2 might prove successful in future clinical trials in a highly selected patient cohort, either with Her2 amplification or Her2 gene mutations. The frequency of Her2 mutations in NSCLC may be too low to justify a prospective clinical trial in this patient group. The frequency of Her2 amplification (2-23%) in NSCLC and the widespread availability of Her2 fluorescence in situ hybridization analysis may justify a final study of trastuzumab monotherapy in this patient population. The role played by Her2 as the obligate heterodimerization partner for the other EGFR family members renders Her2 an attractive target irrespective of receptor overexpression. The most promising Her2-targeted strategy will likely prove to be combinatorial approaches using an EGFR tyrosine kinase inhibitor together with Her2 dimerization inhibitors.