Demonstrating technical competence is a fundamental requirement for any testing or calibration laboratory. Customers, regulators, and accreditation bodies expect laboratories to produce results that are accurate, repeatable, and comparable with those of other competent laboratories. Two important tools used to establish and maintain this confidence are Inter-Laboratory Comparison (ILC) and Proficiency Testing (PT). While these terms are sometimes used interchangeably, they serve different purposes and operate at different levels of formality.