Cytosolic calcium (Ca2+) oscillations are vastly flexible cell signals that convey information regulating numerous cellular processes. The frequency and amplitude of the oscillating signal can be varied infinitely by concerted actions of Ca2+ transporters and Ca2+-binding proteins to encode specific messages that trigger downstream molecular events. High frequency cytosolic Ca2+ oscillations regulate fast responses, such as synaptic transmission and secretion, whereas low frequency oscillations regulate slow processes, such as fertilization and gene transcription. Thus, the cell exploits Ca2+ oscillations as a signalling carrier to transduce vital information that controls its behaviour. Here, we review the underlying biochemical mechanisms responsible for generating and discriminating cytosolic Ca2+ oscillations. (C) 2010 Elsevier Inc. All rights reserved.