This paper outlines the legal system in the United States, the different types of courts, the differences between criminal and civil law, and the role of forensic engineering experts involved in civil lawsuits. After providing a summary of relevant procedures employed by civil and criminal courts, the paper describes the basic principles and requirements for the selection and work of a forensic engineering expert in both the state and federal court system. This paper outlines the role and function of forensic experts (specifically forensic engineers), in the United States court system. It is not a treatise on the legal system but on the role of experts. The paper presents the requirements typically used in today’s legal system to qualify a forensic engineer as an expert witness and to accept his or her work and opinions. Furthermore, this paper discusses who can be an expert witness, the expert’s report, applicable standards, conducted research, engineering opinions, and final testimony in court — and how those elements fit into the legal system. Lastly, the paper describes the concept of spoliation of evidence.