Ecosystem engineers are organisms that modify, maintain and/or create habitat. The term was originally proposed twenty years ago by Clive Jones, John Lawton, and Moshe Shachak in an effort to bridge the largely separate pursuits of population and ecosystem ecology. They proposed a conceptual framework for understanding how organisms modulate resources and thus have the potential to indirectly interact with other organisms. In the relatively short history of the term’s use, ecosystem engineers have inspired tremendous interests from observational, experimental, and theoretical ecologists as well as evolutionary biologists and have influenced work in all ecosystems including marine, freshwater, and terrestrial, as well as in a diversity of living systems from the smallest microbes to the most massive trees. “Ecosystem engineer” is one of several related terms that came to ride a building wave of interest in how organisms can create and modify habitats. “Ecosystem engineer” has been adopted as one of the most popular terms and has helped galvanize research on the topic by giving a common name to a wide variety of mechanisms by which organisms interact with the physical environment (and thereby indirectly affect other organisms), as these interactions did not fit into the common categories of ecological interactions that had previously driven much of contemporary ecological study. Included in the earliest definition is a distinction between “autogenic engineering” in which the structure of the engineering species itself alters the environment, such as tree leaves that fall to the ground and change soil conditions, and “allogenic engineering” in which organisms transform habitats or resources but are not themselves a part of the habitat, such as beavers that dam creeks and create ponds. The term “ecosystem engineer” has experienced a near-exponential growth in the number of publications and citations since its introduction. This body of work has demonstrated the power for ecosystem engineering to explain conspicuous patterns in species abundance, diversity, and ecosystem processes which is a core pursuits of ecology.