“It is not only the species that change evolutionarily through interactions . . . the interactions themselves also change.” Thus states John N. Thompson in the foreword to Interaction and Coevolution, the first title in his series of books exploring the relentless nature of evolution and the processes that shape the web of life. Originally published in 1982 more as an idea piece—an early attempt to synthesize then academically distinct but logically linked strands of ecological thought and to suggest avenues for further research—than as a data-driven monograph, Interaction and Coevolution would go on to be considered a landmark study that pointed to the beginning of a new discipline. Through chapters on antagonism, mutualism, and the effects of these interactions on populations, speciation, and community structure, Thompson seeks to explain not only how interactions differ in the selection pressures they exert on species, but also when interactions are most likely to lead to coevolution. In this era of climate change and swiftly transforming environments, the ideas Thompson puts forward in Interaction and Coevolution are more relevant than ever before.