Calcium (Ca2+), which regulates diverse signaling networks, is one of the most important second messengers in plants. A typical signal is generated by the influx of Ca2+ into the cytosol through influx channel proteins, which then is decoded by Ca2+ binding proteins followed by maintenance of Ca2+ homeostasis driven by efflux transporters. The plant Ca2+ signaling system seems to have evolved differently than Ca2+ signaling pathway in the animal system, yet there is a high level of overlap in functional aspects and processes it modulates. In plants, Ca2+ signaling participates actively to transduce signals for physiological (biotic and abiotic stresses and nutrient sensing) and developmental processes. Recently involvement of Ca2+ in plant memory mechanisms is also being reported. In this chapter, we will describe the significance of the Ca2+ signaling in plants and how it brings specificity in regulating different physiological processes in plants.