The effect of ecological change on evolution has long been a focus of scientific research. The reverse--how evolutionary dynamics affect ecological traits--has only recently captured our attention, however, with the realization that evolution can occur over ecological time scales. This newly highlighted causal direction and the implied feedback loop--eco-evolutionary dynamics--is invigorating both ecologists and evolutionists and blurring the distinction between them. Despite some recent relevant studies, the importance of the evolution-to-ecology pathway across systems is still unknown. Only an extensive research effort involving multiple experimental approaches-particularly long-term field experiments--over a variety of ecological communities will provide the answer.