The verification system of the Chemical Weapons Convention (CWC) is a sophisticated ensemble of systematic and routine on-site inspection measures, and fact-finding mechanisms to address cases of possible non-compliance. Extensive preparations by the OPCW Preparatory Commission, including the development of detailed inspection procedures, the procurement of inspection equipment and the training of the first group of OPCW inspectors ensured an effective start of CWC implementation at the CWC’s entry into force in 1997. Since then, verification methods have been refined to optimize resource utilization and adapt to changes in the implementation environment. Although the fact-finding mechanisms of the CWC were never invoked, the OPCW has created ad-hoc fact-finding mechanisms, in collaboration with the United Nations, to investigate cases of chemical weapons use in Syria. Controversy about the use of chemical weapons by the Syrian armed forces has created political pressure, and there are technical challenges to enhance forensic capabilities in support of attribution of responsibility for CWC violations, in particular the use of chemical weapons. The OPCW has responded to these challenges and created new opportunities to strengthen verification as well as international cooperation, including through the establishment of its Center for Chemistry and Technology.