The timing of plant life-history traits provides the background on which a huge number of ecological relationships and processes depend. Competitive relationships among plants, intertrophic relationships, carbon and water cycles, and other ecosystem functions are all affected by when plants germinate, leaf out, flower, fruit, and senesce. In addition, it is critical to individual plants that they reach particular life history stages at the appropriate time, when the environmental circumstances are right. Moreover, plant phenology is among the most sensitive biological responses to recent climate change. Many spring phenomena across the world are occurring earlier as the climate warms. However, there is incredible variation within this general shift toward earlier leaf out and flowering. For example, some plants are flowering much earlier, other less so, and yet others are flowering at about the same time as they did in the past. The complexity of the changes in plant phenology are impacting ecological and evolutionary processes in equally complex ways. Many ecosystem functions may be disrupted. Thus, it is critical that we understand the phenological changes taking place. This session will feature new research characterizing the variation in plant phenology and phenological responses to climate change. It will highlight evolutionary responses to environmental variation and the impacts that phenological variation has on ecosystems. Speakers will examine plant phenology from ecological and evolutionary perspectives at several scales - from individuals to populations and communities to large regions. This session will provide a good overview of the state of plant phenology studies.