The increasing understanding of the molecular mechanisms of neoplastic transformation and progression has prompted the search for novel drugs that could interfere with the intracellular targets involved in this process. EGFR is implicated in the development and progression of the majority of the common human epithelial cancer; therefore different agents have been developed to block EGFR activation in cancer cells. This review focuses on EGFR-tyrosine kinase inhibitors in clinical practice that interfere with ATP binding, inhibiting tyrosine kinase activity and subsequently blocking signal transduction from EGFR. We report current knowledge on molecular mechanisms underlying the anticancer activity of EGFR-tyrosine kinase inhibitors in preclinical models, with particular attention to EGFR downstream effectors responsible for treatment efficacy or resistance.