There are many kinds of authorization letter. They are used in many situations, but principally to give permissions, approvals and to delegate responsibility. You can write it to authorize a payment, to give a permission either to do or to use something. If part of an organization, you could need it for a study or report, or to attend a seminar or conference. This letter can also be produced to have access to particular files and information. They are very important in business. It can also be used to authorize someone to act on your behalf when, for instance, you are ill, far away or unable to attend a meeting. Another common use of this type of letter is for medical or financial instructions and releases. You may need to write it for medical purposes: for example to have medical records released or to let someone else collect your exams. Or, with a bank, to allow a specific person to do particular operations on your behalf. It is always better to print it on your company letterhead, as it usually is a formal document.
But the format changes depending on the circumstances and the target. Obviously you can find templates on the internet but there are many books dedicated to this topic containing all the necessary instructions and covering all the situations to create a well formatted autorhization letter. First of all, it is necessary that you state clearly what you want or do not want, avoiding any doubt or confusion. It is also fundamental that you use the adequate language to the situation, and that you give all the necessary instructions and details. For example a legal document has a very different language from a scientific one, so it is necessary that the receiver understands the full meaning of the content and, above all, the intention of the letter. An authorization letter can have different purposes from business or professional ones. It can be used in schools as well as in everyday life.
When you write (or receive) this kind of letter, you must be sure that all the identification information are correct, clear and doubtless. Pay always attention: it is legally valid only if signed. Basicly, it must always be clear and doubtless for the reader/receiver what to do, when to do and how the reader can accomplish the task. Every detail has to be covered. Especially if there is a deadline to be respected. The more explicit it is, less later corrections are needed. They may also be required to let someone else, or an organization, to pick up your passport, or any other personal document. Some authorities require an authorization letter to allow you to live and work in their country. So, do not forget to follow all the step detailed to write an authorization letter by yourself or to check the validity of one that you receive. Remember to pay always a great attention to the right format and grammar. And, if requested, to write it on a letterhead paper.