Locard is renowned for his Theory of Exchange. This principle, often referred to as Locard's Exchange Principle, is a foundational concept in forensic science. It posits that whenever two objects come into contact, there is a mutual exchange of materials between them. This principle underlines the idea that criminals will invariably leave traces at a crime scene, and similarly, they will carry away evidence from the site. This fundamental notion is crucial for forensic investigations, enabling experts to analyze such material exchanges to uncover links between suspects, victims, and crime scenes.