Phenology is the study of recurring events in nature and their relationships with climate. The word derives from the Greek phaínō ‘appear’ and logos ‘reason’, emphasizing the focus on observing events and understanding why they occur (Demarée and Rutishauser 2009). Phenological recording has a history that dates back many centuries (Linneaus and Bark 1753; Aono and Kazui 2008). More recently, advances in monitoring technologies have enabled automated and remotely sensed observations, complemented by increasing citizen science participation in monitoring efforts. Phenological information can also be derived from widespread environmental monitoring stations around the globe. Phenological records clearly demonstrate the biological effects of year-to-year variability in climate, as well as longer-term trends associated with environmental change. Phenological monitoring thus plays an important role in understanding how our planet is changing. Changes in the growing season, for example, are more tangible and more readily conveyed to the general public than seemingly small changes in mean annual temperature. Here, we describe just a fraction of the phenological information currently available, highlighting northern hemisphere records of phenology of primary producers across a range of spatial and temporal scales.