Abstract: Boron (B) is an essential mineral nutrient for higher plants. However, its physiological role in plants and its molecular mechanism are still not well understood. This paper summarizes substantial progress achieved in recent years and unresolved questions. The molecular mechanisms of B cross-linking with rhamnogalacturonan II (RG-II) to form B-RG-II complex and its important role in the development and stability of the cell wall was verified. Moreover, the enhanced formation of B-RG-II seems to be closely related to the conquering of land during plant evolution. As well, genetic engineering has confirmed that the first B transporter, BOR1, involved in xylem loading and cloned in Arabidopsis, and NIP5;1, a member of the major intrinsic protein family, function as a boric acid channel for B uptake and are crucial for plant growth and development under B limitation in Arabidopsis. Finally, some valuable germplasms for high B-utilization efficiency were screened in rapeseed, wheat, and barley, and the mapping and cloning of quantitative trait loci for tolerance to B deficiency or B toxicity are in good progress.