In recent years evidence has been presented that implicates the role of free (cytosolic) Ca2+ as a major metabolic and developmental controller in plants. Calcium concentrations in the cytoplasm are kept very low under normal conditions (10-6 to 10-8 M). Small changes in the absolute amount of calcium can create a 10- to 100-fold change in the Ca2+ concentration without upsetting the ionic balance of the ceil. This feature makes Ca2+ an excellent candidate as a second messenger. Thus, a stress induced change in the cytosolic Ca2+ could bring a cellular/plant response to stress. This response is thought to be mediated through activation of Ca2+ and/or Ca2+-calmodulin-dependent protein kinases which in turn mediate the activity of various enzymes via phosphorylation. Recent evidences from the impact of salinity, low temperature, high temperature, and biotic stresses support such a role of calcium. Data on the association between stress-induced injury and perturbation of membrane/cytosolic calcium are available. In addition, evidences for the role of calcium in acclimation to stress have been reported. These studies suggest that manipulation of cellular Ca2+ may be one of the approaches we have on hand to bridge the gap between science and technology.