A growing, but little understood area of Government involvement in promoting renewable energy, is the use of demonstration projects and field trials (DTs) as a policy tool. This paper explores the historical role of DTs in the commercialisation of wind turbines. We review information from government, academic and industry sources, together with the newly created Cass Wind DT database, and consider the context, objectives, participants and nature of wind DTs in the EU, US and Japan. Overall, it is difficult to identify the benefits of wind DTs for many of the key actors. Government funding of DTs does not appear to be shaped by coherent or targeted strategic objectives-indeed governments use DTs differently despite similar stated objectives. A common theme has been the involvement of many stakeholders, with local authorities, utilities and operators taking the lead rather than manufacturers. Wind DTs appear to have neither enabled participating manufacturers to become significant global suppliers-with a few exceptions driven by additional financial and legislative support from national governments-nor to have established a dominant design. The major benefit of wind DTs; appears to have been 'learning by using' for utilities and wind farm operators, reducing operational costs. (C) 2009 Elsevier Ltd. All rights reserved.