The multiple-nuclei theory is a theory of urban growth developed by Chauncy Harris and Edward Ullman that views the growth of cities as emerging from many centers of development or "nuclei," rather than expanding outward from a single central business district as suggested by the concentric-zone theory. This theory posits that a city may have several distinct centers of activity, each specializing in a particular urban need or activity, such as a retail district, a manufacturing area, a residential suburb, or a university campus. The development of these multiple nuclei is influenced by factors such as the availability of land, transportation routes, the clustering of similar industries or activities, and the avoidance of incompatible land uses. The multiple-nuclei theory provides a more complex and realistic model of urban structure, particularly for large, sprawling cities that have developed over time and have multiple centers of economic and social activity.