A private investigator (PI) is a professional who conducts investigations to gather information for clients. They often work on cases involving infidelity, missing persons, or background checks. PIs use various techniques, including surveillance, interviews, and research, to uncover facts and evidence. Private investigators can be hired by individuals, businesses, or attorneys. They may also assist in legal matters, such as criminal defense or civil litigation. While some PIs work independently, others are part of agencies. Most states require PIs to have a license, which often involves background checks and training.