Boron (B) is an essential nutrient for vascular plants with a key role in the stabilization of the primary cell wall through the formation of borate esters with apiose residues of rhamnogalacturonan II. B limited availability in soil and irrigation water affects the yield and quality of crops, which produced significant economic losses. This fact highlights the importance of understanding not only the role of B in plants, but also the physiological and molecular responses and tolerance mechanisms to B deficiency. In recent years, several studies have contributed greatly to the knowledge of these subjects. This will allow the development of crop plants that more efficiently use B and, therefore, are more tolerant to B deficiency. In this chapter, all these aspects related to B are addressed in a comprehensive manner.