This document discusses clusters, which are groups of geographically proximate firms in related industries and institutions. Clusters arise naturally from things like resources, demand, and entrepreneurship, and evolve over time rather than being constructed. They benefit firms through mechanisms like knowledge spillovers, specialized inputs, and skilled labor pools. This increases innovation and competitiveness. However, clusters experience inefficiencies like knowledge and network failures that can inhibit innovation, so there is a need for policy support to address gaps between different entities within clusters.