Type 2C protein phosphatases (PP2Cs) form a structurally unique class of Mg2+-/Mn2+-dependent enzymes. PP2Cs are evolutionary conserved from prokaryotes to higher eukaryotes and play a prominent role in stress signalling. In this review, we focus on the evolution, function and regulation of the plant PP2Cs. Members of a subclass of plant PP2Cs counteract mitogen-activated protein kinase pathways, whereas members of other subfamilies function as co-receptors for the phytohormone abscisic acid. Recent structural analyses of abscisic acid receptors have elucidated the mode of ligand-dependent regulation and substrate targeting.