Chain of custody is a legal term that refers to the chronological documentation or paper trail that records the sequence of custody, control, transfer, analysis, and disposition of materials, including physical or electronic evidence. It is a process used to track the movement and control of an asset through its lifecycle by documenting each person and organization who handles an asset, the date/time it was collected or transferred, and the purpose of the transfer. The chain of custody is the most critical process of evidence documentation, and it is a must to assure the court of law that the evidence is authentic, i.e., it is the same evidence seized at the crime scene, and it was, at all times, in the custody of a person designated to handle it and for which it was never unaccounted.

Establishing the chain of custody is essential for the forensic scientist that is working on a specific criminal case. The documentation of evidence is key for maintaining a chain of custody because everything that is done to the piece of evidence must be listed, and whoever came in contact with that piece of evidence is accountable for what happens to it. This prevents police officers and other law officials from contaminating the evidence or taking the piece of evidence.

Chain of custody is used in most chemical sampling situations to maintain the integrity of the sample by providing documentation of the control, transfer, and analysis of samples. It is also used in security and risk mitigation for critical infrastructure sectors and their assets.

In summary, the chain of custody is a process that tracks the movement of evidence or assets through its collection, safeguarding, and analysis lifecycle by documenting each person who handled the evidence, the date/time it was collected or transferred, and the purpose for any transfers. It is critical in forensic practice and legal contexts to maintain the integrity of the evidence and assure the court of law that the evidence is authentic.