Parties in patent lawsuits that are going to trial face a crucial choice: who is the best witness to explain the often complex or scientific technology behind an invention or an accused product? Often, the parties will select an employee witness such as an engineer, scientist, or a named inventor of the patent-in-suit to offer this key testimony rather than a hired expert. Many litigants have found that there are benefits to choosing an employee witness who can testify based on first-hand experience with the technology in question rather than a hired expert, who must prepare an expert report and may not have the same incentives as the litigant. But when litigants offer such employee witnesses as lay rather than expert witnesses, courts have struggled to define the precise boundaries of lay versus expert testimony under the Federal Rules of Evidence. This has created a growing conflict among courts over how far a lay witness may go in testifying about technical and scientific matters in patent trials when the subject of the witness’s testimony comes from first-hand knowledge. This paper addresses these conflicting cases and proposes an approach that courts can use to determine which subjects are appropriate matters only for expert witnesses and which subjects can be addressed by highly skilled and knowledgeable lay witnesses.