Control of cell growth and differentiation has long been a focus of intense research interest, particularly in the context of cancer therapeutics. The evolutionarily-conserved extracellular signal-regulated kinases 1 and 2 (ERK1/2) are serine-threonine kinases that respond to a wide range of mitogens and growth factors to initiate changes in cellular proliferation and differentiation, and are the most important members of the mitogen-activated protein kinase (MAPK) family in terms of seven transmembrane-domain receptor (7TMR)-mediated regulation of mitogenic processes. Regulation of the ERK1/2 signaling cascade by 7TMRs is highly complex and cell type-specific. Recent advances in our knowledge of this effector pathway have revealed that its regulation is at least partly independent of traditional G protein-mediated actions arising from the stimulation of 7TMRs. This review summarizes the current position of our knowledge of ERK1/2 regulation, and illustrates the wealth of potential targets available for the development of new strategies for the treatment of proliferative and other ERK-related disorders.