Abiotic stresses such as extremes in water, temperature, and salinity are major limiting factors for the productivity of most crops. The plant response and adaptation to these stresses are controlled by numerous small-effect loci and regulated by hundreds of genes controlling various developmental and physiological processes. The elucidation of the abscisic acid (ABA) functional mechanisms in mediating the response and adaptation to stresses as described in the previous chapters has provided many opportunities for the development of new crop varieties with enhanced stress resistance. In this chapter, we mainly focus on the recent studies of ABA-related genes (involved in metabolism, signaling, and regulation) that have been well characterized and are known to affect stress resistance and especially those genes which have been engineered in crops for stress resistance improvement. Although there is evidence that many ABA-related genes have a biologically significant effect in improving stress resistance, a large gap remains to generate crops with significantly improved stress resistance in the field. A significant challenge is to unveil the complex mechanisms of stress resistance in crops by more intensive and integrative studies to find the key functional components involved in the ABA-mediated biological processes as tools for engineering and breeding stress-resistant crops.