Approve means to validate something or to give consult for some act to be done. A letter of approval is a written consent by a regulatory authority or body to proceed with an activity that is requested by someone. Therefore; this letter can serve as a certification or registration. An approval letter can be of two types: in first place it would be simply for granting approval of something, whereas; in second place an individual or organization can write a letter seeking for approval for something, in this second capacity it is commonly termed as request for letter of approval.
A letter of approval can be written for a number of reasons. Some common uses are to give permission at work (vacation, expenditure or sickness leave), to endorse a project, financial approval or a loan. An approval letter is written in response to a request made by an employee or a team of the organization. If the employer of the manager of the organization feels that such a request is reasonable and should be entertained by giving approval, he then writes an approval letter. If any kind of further actions are requested by the person, letter addresses to, it should be started clearly. If the approval is contingent on a time limit, it should be mentioned, for example the date on which the task will start or till the date it will continue.
As it is an important document, so it should be drafted carefully. This letter is a formal document so the tone of the approval letter should be professional and communicative. The general tone should be warm; it should be free from grammatical, spelling or punctuation errors. It should be having a clear line for what has been approved and to what extent. If there are any restrictions implied to this approval it should be mentioned. The letter should be ended with a congratulatory tone, signed and stamped. You can also get help from the attached samples of approval letters.