Certified reference materials (CRMs) are substances or materials with a known composition and properties, used to calibrate instruments and validate analytical methods. They ensure accuracy and reliability in measurements across various fields, including chemistry, biology, and environmental science. CRMs are produced under strict quality control and are accompanied by a certificate that details their specifications. These materials play a crucial role in quality assurance and compliance with standards set by organizations like the International Organization for Standardization (ISO) and the National Institute of Standards and Technology (NIST). By using CRMs, laboratories can maintain consistency and trust in their testing results, ultimately enhancing the credibility of their work.