Flooding is a major problem in many crop areas around the world. However, many wetland plant species can expand their roots into flooded soils because of the presence of longitudinal aerenchyma channels that facilitate oxygen diffusion from the shoots to the root tips. Aerenchyma also forms in rice roots, allowing rice plants to grow well in flooded paddy fields. Aerenchyma formation therefore helps plants to survive flooding. “Primary aerenchyma” forms in the roots of some cereal crops such as rice, maize, barley and wheat. “Secondary aerenchyma” forms in the stem, hypocotyl, tap root, adventitious roots, and root nodules of some legume crops such as soybean. This paper reviews the recent progress in the study of aerenchyma formation, and highlights the role that primary aerenchyma in cereal crops and secondary aerenchyma in soybean can play in improving their tolerance to flooding.