This document discusses different forms of industrial agglomeration and clustering. It describes how industries can cluster in three main ways - through the enlargement of an individual industrial plant, clustering of related industries, or clustering of unrelated industries. It provides examples of each type of clustering. The document also discusses the internal and external economies of scale that industries gain from clustering in a particular area, such as access to shared infrastructure, labor pools, and ancillary services. Finally, it notes that once industries are established in a certain location, there is inertia to remaining there even if the original benefits disappear, due to costs of relocating.