The Cluster Initiative Greenbook, prepared for the 6th Global TCI Conference, takes a closer look at CIs around the world, mainly in OECD countries. It is built on a unique data-set of over 250 cluster initiatives, derived from the 2003 Global Cluster Initiative Survey and a series of case studies. Industrial clusters have important knowledge sharing implications, and their development marks movement towards a knowledge economy. http://www.cluster-research.org