A Certificate of Sponsorship (CoS) is a document issued by licensed sponsors in the UK to support visa applications for skilled workers from overseas. It serves as proof that a job offer has been made to a migrant worker and that the position meets the required criteria for sponsorship. Employers must obtain a CoS from the UK Visas and Immigration (UKVI) before sponsoring a migrant worker under the Skilled Worker Visa route or other eligible visa categories. The CoS contains information about the job, the employer, and the prospective employee and is essential for the visa application process.