Several crystal andNMRstructures of calmodulin (CaM)in complex with fragments derived from CaM-regulated pro-teins have been reported recently and reveal novel ways for CaMto interact with its targets. This review will discuss and compare features of the interaction between CaM and its target domains derived from the plasma membrane Ca 2+ -pump, the Ca 2+ -activated K + -channel, the Ca 2+ / CaM-dependent kinase kinase and the anthrax exotoxin.