Calcium (Ca²⁺) is an almost universal intracellular messenger, controlling a diverse range of cellular processes, such as gene transcription (see Mellström and Naranjo, this issue), muscle contraction and cell proliferation. The ability of a simple ion such as Ca²⁺to play a pivotal role in cell biology results from the facility that cells have to shape Ca²⁺signals in the dimensions of space, time and amplitude. To generate the variety of observed Ca²⁺signals, different cell types employ components selected from a Ca²⁺signalling ‘toolkit’, which comprizes an array of signalling, homeostatic and sensory mechanisms. By mixing and matching components from the toolkit, cells can obtain Ca²⁺signals that suit their physiology.