The paper examines the views, often associated with Porter, that clusters with deep collaborative networks and established local supply chains have good performance. The view that good cluster performance is not connected to the industrial sector is also assessed. Data from a Department of Trade and Industry (DTI) study on UK clusters are used to assess the impact on performance (employment growth and international competitiveness) of cluster depth, the stage of development of local supply chains, and industrial sector. The results of the analysis of the DTI data on clusters do not provide strong support for Porter-type views on cluster policy. Although established clusters are linked to employment growth, deep clusters are not associated with employment growth or international competitiveness, and clusters in the services, and media, computer-related and biotechnology sectors are more likely than manufacturing clusters to have good performance. Some of the major policy implications of the results are discussed in the light of the literature on the importance of regional, national, and international networks for the performance of clusters.