In response to the alarming growth in autism diagnoses, Congress passed the Combating Autism Act of 2006 (P.L. 109-416), which established the Interagency Autism Coordinating Committee (IACC) to coordinate all efforts within the U.S. Department of Health and Human Services related to ASD. The Combating Autism Act requires that, in addition to several other key responsibilities, the IACC must prepare an annual summary of advances in autism research. The 2008 IACC Summary of Advances highlights 37 significant studies on autism spectrum disorder selected by members of the IACC. A bulleted overview of the major findings in 2008 is followed by a more detailed description of the scientific breakthroughs in each category. Information about funding sources and journal impact factor scores is included in a table at the end of the document. This year's advances are sorted into six topic areas that correspond to six critical questions for those affected by ASD: (1) Diagnosis: When should I be concerned?; (2) Biology: How can I understand what is happening?; (3) Risk Factors: What caused this to happen and can this be prevented?; (4) Treatment: Which treatments and interventions will help?; (5) Services: Where can I turn for services?; and (6) Outcomes: What does the future hold? (Contains 54 footnotes.)