Arsenic is a toxic metalloid contaminating soil and water supplies in many regions worldwide, and its entry into the food chain poses a serious health risk to millions of people. Arsenic is toxic to plants, lowering the rate of photosynthesis and inhibiting growth, resulting in a reduction in crop yields. Therefore, there is a pressing need to improve arsenic tolerance in plants and reduce accumulation of arsenic in crops. To this end, an arsenite efflux transporter from yeast was heterologously expressed in rice plants under the control of tissue specific promoters. Expression in different tissues led to altered arsenic tolerance and tissue distribution, indicating that this is a promising strategy for the future development of arsenic tolerant varieties. The role of NIP aquaporins in arsenic transport and tolerance in the model plant Arabidopsis was explored in Chapter 3. Group II NIPs were identified as relevant targets for engineering arsenic tolerance and reducing seed/grain arsenic accumulation in crops. Further targets for engineering arsenic tolerance were identified from a collection of T- DNA insertion mutants of Arabidopsis using forward and reverse genetic screening approaches. Two of these were further characterised for their role in arsenic tolerance and accumulation.