Salinity stress has a major impact on plant growth and development. Increasing concentrations of salt in farm soils means that researchers must develop tolerant crops if the global food supply is to be sustained. Salt adaptation involves a complex network of different mechanisms whose responses to high salinity are regulated in an integrated fashion. The salt-stress signaling cascade(s) that activates these mechanisms starts by perceiving the saline environment. However, little is known about the components involved in either the perception or signaling of this stress. The mechanisms that are activated under such conditions include those responsible for ion homeostasis and osmotic adjustment. Here, we review the current understanding of those molecular mechanisms used by plants to respond and adapt to salt stress. Particular attention is paid to the information yielded by genetic analyses of the yeast model Saccharomyces cerevisiae and the higher-plant model system of Arabidopsis.