Health care fraud and abuse cases are often won or lost on the effective use of expert witnesses. As health care fraud cases have become more complex and technical, the scope and use of expert testimony has proliferated, and the successful use of experts is one of the lawyer's most important jobs. False Claims Act, Anti-Kickback Statute, and Stark Law cases all demand various types of experts to assist the trier of fact in understanding the nature of the case, the morass of rules at play, the evidence, and a variety of billing, valuation, contractual, technical, and compliance concepts. Increasingly, expert reports and testimony play a pivotal role in motions for summary judgment, as well as at trial. Experts also are used in "conference room litigation," such as mediations or negotiations between defense counsel and enforcement agencies. This article is the result of interviews with health care fraud litigators and expert witnesses in the field who identified their best practices to produce optimum outcomes for their clients.