Confirmation of Acceptance for Studies (CAS) is a very significant paper that you need to know about if you plan to study in the UK. Before you apply for a UK Student Visa (Tier 4 General), you must have a CAS letter. CAS is an electronic document that you received from the college or university at which you chose to study. Your CAS will be applicable for six months from the time of issue for a student visa request. Your institution will also provide you with a unique reference code that matches your CAS. You must mention this code on the request document for a Tier 4 visa. This code and corroborating paper will be checked by the formal visa handling department to verify you have an unconditional university grant. The data they used to produce your CAS will also be sent by your college. This is called a' CAS declaration' and will be sent by email to you. For your Tier 4 visa implementation, the CAS declaration is not needed but it provides all the data about your class and partner as well as some cash data you need to finish your Tier 4 visa request process.