The Environmental Protection Agency (EPA or the Agency) established in 2000 new far reaching emission standards beginning in 2007 for heavy-duty diesel vehicles and the fuel used in them. These standards were premised on the introduction of new catalyst based emission controls for diesel engines and the removal of a catalyst poison, sulfur, from diesel fuel. This report is the second in a series of technical progress reviews by EPA to document the status of engine and vehicle technology development to meet the 2007 standards. The first report, published in June of 2002, concluded that progress to that time had been substantial and was in keeping with the expected progress necessary for successful implementation of the new standards in 2007. This second report also considers the continuing progress in the research laboratory but, more importantly, the transition of these technologies from research into business plans, product development programs, engines and vehicles for field testing, and finally into real products for sale in the marketplace in 2007. Thus, while we continue to be impressed by the amount of technical progress shown in the laboratory, it is the concrete steps that manufacturers have taken in their new product development programs that gives us great confidence for 2007.