Opuntia spp. is an economically important crop from the Cactaceae family and native to the tropical and subtropical regions of America. It is cultivated for various uses such as fresh fruit, pharmaceutical, cosmetic, or in the form of beverage. Opuntia spp. is well known for its anatomical and physiological characters to conserve water and tolerate extreme drought conditions. The production of Opuntia has been extended around the world and it has become an alternative crop in the areas with low-quality soil and water deficit. The ability to tolerate the extreme environments of Opuntia species makes them also valuable to study molecular mechanisms underlying abiotic stress tolerance. Opuntia is crassulacean acid metabolism (CAM) species with high water-use efficiencies (WUE) that makes it to be able to grow in areas with insufficient precipitation and less water availability to support traditional C3 or C4 bioenergy crops. Studies of photosynthesis have shown that these species use a particular photosynthetic pathway known as CAM for the fixation of atmospheric CO2 during the dry season. Indeed, in the CAM pathway as an adaptation mechanism in plants to water deficit, all or part of the atmospheric CO2 uptake occurs at the nighttime that remains stomata closer at daytime when the temperature is a higher and consequent reduction in the evapotranspiration rates. Atmospheric CO2 uptake ratio can affect the biomass production in plants. Despite, CO2 fixation in CAM plants is 15% more efficient than C3 plants, CAM species often grow slowly due to their extra enzymatic reactions for carbon fixation. In C3 plants, 3 ATP and 2 NADPH require for each CO2 molecular fixation, while in CAM plants for each CO2 fixation, 5.5–6.5 ATP and 2 NADPH are required. In CAM plants net carbon fixation efficiency is 10% less than C4 plants. However, under optimal growth conditions, Opuntia has the potential to produce higher biomass rivaling that of C3 and C4 crops. Moreover, growth character and CAM pathway in genera Opuntia, allow these species to operate at near-maximum productivity with relatively low water requirement. Cultivation of CAM species from the genera Opuntia can provide an alternative to product feedstocks and food in the arid and semiarid regions. For this purpose, here in this chapter, we will discuss (a) the crassulacean acid metabolism pathway; (b) the molecular mechanism of CAM; (c) physiological attributes of CAM during the drought tolerance period; (d) CAM improve Opuntia biomass production. Furthermore, screening Opuntia species that qualify with water use efficiency and high productivity will be interesting to be reviewed in this chapter to provide the alternative feedstock bioenergy crops that preserve and expand feedstock production in water-limited areas.