A Certificate of Sponsorship is not a physical document — it is an electronic record assigned via the Sponsor Management System (SMS). Each CoS is tied to a specific job, employer, and worker. There are two types: defined CoS (for out-of-country applications) and undefined CoS (for in-country applications, such as switching visa routes). The Home Office allocates CoS to employers in batches. The CoS contains details of the job offer including role, salary, and start date. A CoS does not guarantee a visa will be granted.