Peter Raven is a student of plant systematics, evolution and ecology, and an active conservationist. He has done important work on the cytogenetics of plant evolution, folk taxonomy, pollination biology and biogeography, especially of the southern hemisphere. With Paul Ehrlich ForMemRS, he developed the theory of coevolution and named the phenomenon in the early 1960s.

One of the first to apply a consideration of plate tectonics to the interpretation of distributions of plants and animals around the world, Peter published a fruitful series of papers in this area from during the 1970s and early 1980s. He served as Co-Editor of the Flora of China, bringing the 49-volume work to completion in early 2014. Over a period of 39 years, he led the Missouri Botanical Garden to become a world force in plant systematics and conservation.

Peter has been an important influence in the area of conservation and the attainment of sustainability, widely emphasising the roles of population, consumption, and technology in driving species extinction and climate change.