Terpenoids, or isoprenoids, comprise the largest and most structurally diverse class of organic compounds. Terpenoids have a multitude of ecological functions, which might be perturbed under changing environmental conditions. The best-known functions of terpenoids are related to adaptation to abiotic stresses and biotic stressors, such as herbivores and pathogens. Volatile and reactive plant terpenoids may also affect the air quality. The volatility of terpenoids provides, for sessile plants, a tool for communication with other organisms, such as neighboring plants, pollinators, and foes of herbivores, via air-borne infochemicals. Carotenoids are tetraterpene pigments that protect the photosynthetic machinery of green plants but also act as visual signal compounds for pollinators and plant-feeding animals. Plant carotenoids are necessary antioxidants for all animals and humans. We review the main properties of biogenic terpenoids from various scales, including the plant cell, leaf surface, and canopy. We also explore links to ecological functions and atmospheric behavior, including the chemical transformations of terpenoids. The functionality of the terpenoids could be strongly influenced by the predicted changes of climatic conditions upon proceeding global climate change. On the other hand, volatile terpenoids released by large, forested areas continue to have a significant effect on local climatic conditions, e.g., by the formation of light-scattering blue haze composed of terpenoid-derived secondary aerosol particles. Such processes might also be altered by climatic changes, leading to further disturbances in ecosystem function.