Leaf wettability, indicating the affinity for water on the leaf surface, is a common phenomenon for plants in a wide variety of habitats. The contact angle (θ) of water on leaves measured at the gas, solid and liquid interface is an index of surface wettability, θ＜110° for hydrophilic and θ＞130° for hydrophobic. The main factors affecting leaf wettability include the wax content and crystal forms, the number and distribution of trichomes, and the shape and size of stomata and epidermal cells. The chemical composition and structure of leaf surfaces are internal causes, but the external environment can also influence wettability by affecting the structure and composition of the surface. The main ecological functions affected by leaf wettability are photosynthetic rate, interception of precipitation, pathogen infection and environmental quality. Precipitation interception on foliage surfaces is affected by high wettabilty as water droplets form a layer of film on the surface that is relatively easy retained on leaves. For low wettability or water-repellent leaves, water on the surface produces droplets that are more easily removed by wind and gravity. The spreading water film on leaves with high wettability can decrease photosynthesis due to high CO₂ diffusion resistance through water to stomata. Differences in leaf wettability can influence the amount of air pollutants that can be captured, absorbed, and filtrated by leaf surfaces; however, if air pollutants injure the leaf surface, a dramatic change in leaf surface wettability may result. For bacterial pathogens, a completely wettable leaf surface can make the leaf more susceptible to infection. Once the bacteria are disseminated, leaf wettability is changed, and may have some impacts on the retention of pesticide droplets used for disease control. Leaves with low wettability repel water and show some self-cleaning characteristics. Some new biomimetic functional materials are designed or manufactured on the basis of plant leaf surface properties with higher hydrophobic materials to enhance leaf self-cleaning. Wettability as a comprehensive response at the solid, gas and liquid phase interface of leaves and as such is important for understanding ecological functions of plants.