This Executive Summary of the Advanced Collaborative Emissions Study (ACES) summarizes the main findings of emissions and health testing of new-technology heavy-duty diesel engines capable of meeting US 2007/2010 and EURO VI/6 diesel emissions standards. The results demonstrated the dramatic improvements in emissions and the absence of any significant health effects (especially cancer). ACES was the most comprehensive examination done to date of engines meeting the US 2007 and 2010 on-road standards. This Executive Summary presents the main findings of all three phases of the project and places the results in the context of health risk assessment, noting that "the overall toxicity of exhaust from modern diesel engines is significantly decreased compared with the toxicity of emissions from traditional-technology diesel engines." Links to all ACES reports are provided below.