Vapor intrusion—migration of volatile chemicals from contaminated groundwater or soil into an overlying building—is now part of nearly every site investigation and many real estate transactions. As the science of vapor intrusion continues to evolve and states continue to update their guidance, professionals involved in vapor intrusion sites need to stay on top of it all. What is the process for a vapor intrusion investigation? What is the science behind such an investigation? How will these new regulations influence such investigations? On September 6, 2012, ELI convened an expert panel to discuss the science of vapor intrusion, how vapor intrusion investigations are completed, new and anticipated guidance and regulations at the state and federal levels, and case studies of various vapor intrusion investigations.