Abstract: Plants living in wetlands or waterlogged environments usually have well-developed aerenchyma. This paper reviews the research in the field, especially morphology and molecular biology, to illustrate the formation of aerenchyma, its physiological functions, inducing factors and enzymes involved in the process. In short, programmed cell death (PCD) is shown to be the mechanism involved in lysigenous aerenchyma formation by the phytohormone ethylene. Ethylene has a crucial role by activating signal transduction in the whole network.