Abstract: Toxicity of ionic aluminum (Al) to the plant root is a major limiting factor for crop production in acid soils. Barley is the most Al-sensitive species in the poaceae. Variations in Al tolerance were observed in different barley cultivars. A dominant gene (Alp) responsible for Al tolerance in barley was identified on the long arm of chromosome 4 as revealed by genetic analysis. The present review highlights the recent progress made over the past several years on the mechanism of Al tolerance in barley, including cloning and functional analysis of the Al tolerance gene Alp, and functional comparison of the Al tolerance genes in other cereal crops as well.