Mitogen-activated protein kinase (MAPK) pathways transfer information from sensors to cellular responses in all eukaryotes. A surprisingly large number of genes encoding MAPK pathway components have been uncovered by analysing model plant genomes, suggesting that MAPK cascades are abundant players of signal transduction. Recent investigations have confirmed major roles of defined MAPK pathways in development, cell proliferation and hormone physiology, as well as in biotic and abiotic stress signalling. Latest insights and findings are discussed in the context of novel MAPK pathways in plant stress signalling.