Arsenic (As) is a non-essential element toxic to plants. Contamination in the environment occurs in many regions, and its accumulation in food crops may pose a health risk to humans. Recent progress in understanding the mechanisms of As uptake and metabolism in plants is reviewed. Arsenate is taken up by phosphate transporters. A number of aquaporin nodulin26-like intrinsic proteins (NIPs) can transport arsenite, the predominant form of As in reducing environments. In rice, arsenite uptake shares the highly efficient silicon pathway of entry to root cells and efflux towards the xylem. In root cells, arsenate is rapidly reduced to arsenite, which is effluxed to the external medium, complexed by thiol peptides or translocated to shoots. One type of arsenate reductase has been identified, but its in planta functions remain to be investigated. Some fern species in the Pteridaceae family are able to hyperaccumulate As in above-ground tissues. Hyperaccumulation appears to involve enhanced arsenate uptake, decreased arsenite-thiol complexation and arsenite efflux to the external medium, greatly enhanced xylem translocation of arsenite, and vacuolar sequestration of arsenite in fronds. Current knowledge gaps and future research directions are also identified. Arsenate uptake is mediated by phosphate transporters, while arsenite uptake is mediated by aquaporin channels. Arsenite efflux is also mediated by aquaporin channels. Arsenite is taken up by plant roots and transported to the xylem. Methylated As species, such as MMA and DMA, are found in some soils but are usually minor As species. They may originate from past use of arsenical pesticides or be synthesized by soil microorganisms. MMA and DMA can be taken up by plants, but generally less efficiently than inorganic arsenate or arsenite. The mechanisms of MMA and DMA uptake by plant roots are unknown. Arsenite efflux from plant roots is a detoxification mechanism, as has been shown for microbes. The role of mycorrhizal fungi in As uptake and resistance is discussed. Arsenate reduction in plants is mediated by ACR2 proteins. Arsenite complexation and sequestration by thiol compounds such as GSH and phytochelatins is an important mechanism of As detoxification. The vacuolar sequestration of arsenite is also important for As detoxification. The role of PCs in As detoxification is discussed. Transgenic plants overexpressing PC synthase genes or the genes involved in the synthesis of the PC precursor GSH may be more tolerant to arsenate or arsenite. The cellular and subcellular distribution of As in nonhyperaccumulator plants is discussed. The vacuolar sequestration of arsenite is important for As detoxification. The role of vacuolar transporters in As detoxification is discussed.Arsenic (As) is a non-essential element toxic to plants. Contamination in the environment occurs in many regions, and its accumulation in food crops may pose a health risk to humans. Recent progress in understanding the mechanisms of As uptake and metabolism in plants is reviewed. Arsenate is taken up by phosphate transporters. A number of aquaporin nodulin26-like intrinsic proteins (NIPs) can transport arsenite, the predominant form of As in reducing environments. In rice, arsenite uptake shares the highly efficient silicon pathway of entry to root cells and efflux towards the xylem. In root cells, arsenate is rapidly reduced to arsenite, which is effluxed to the external medium, complexed by thiol peptides or translocated to shoots. One type of arsenate reductase has been identified, but its in planta functions remain to be investigated. Some fern species in the Pteridaceae family are able to hyperaccumulate As in above-ground tissues. Hyperaccumulation appears to involve enhanced arsenate uptake, decreased arsenite-thiol complexation and arsenite efflux to the external medium, greatly enhanced xylem translocation of arsenite, and vacuolar sequestration of arsenite in fronds. Current knowledge gaps and future research directions are also identified. Arsenate uptake is mediated by phosphate transporters, while arsenite uptake is mediated by aquaporin channels. Arsenite efflux is also mediated by aquaporin channels. Arsenite is taken up by plant roots and transported to the xylem. Methylated As species, such as MMA and DMA, are found in some soils but are usually minor As species. They may originate from past use of arsenical pesticides or be synthesized by soil microorganisms. MMA and DMA can be taken up by plants, but generally less efficiently than inorganic arsenate or arsenite. The mechanisms of MMA and DMA uptake by plant roots are unknown. Arsenite efflux from plant roots is a detoxification mechanism, as has been shown for microbes. The role of mycorrhizal fungi in As uptake and resistance is discussed. Arsenate reduction in plants is mediated by ACR2 proteins. Arsenite complexation and sequestration by thiol compounds such as GSH and phytochelatins is an important mechanism of As detoxification. The vacuolar sequestration of arsenite is also important for As detoxification. The role of PCs in As detoxification is discussed. Transgenic plants overexpressing PC synthase genes or the genes involved in the synthesis of the PC precursor GSH may be more tolerant to arsenate or arsenite. The cellular and subcellular distribution of As in nonhyperaccumulator plants is discussed. The vacuolar sequestration of arsenite is important for As detoxification. The role of vacuolar transporters in As detoxification is discussed.