The ErbB family of receptor tyrosine kinases serves as a model for understanding the propagation of growth factor signals across the plasma membrane and the interpretation of those signals into a cellular response. Recent studies point to a critical role for the accumulation of ErbBs at specific cell-surface locations in the fidelity of ErbB signaling. The past year has witnessed significant advances in our understanding of the molecular mechanisms of ErbB localization and the role of PDZ-domain-containing proteins and cell-surface glycoproteins in directly modulating signaling through ErbBs.