Some countries, such as Canada and the United States, may require the visitor to receive a letter of invitation upon visa application. An invitation letter is a formal letter from the person you wish to visit, which states that they invite you to visit them in that country. Invitation letters help travel authorities verify potential visitors by ensuring that a temporary visit is the true nature of the visa application. On the government website of your destination, find out about the details of what should be in such a letter. The U.S. passport has a mobility rating of 166, which means owners can visit 156 countries without a visa. You can find the complete list in our Passport Index. These Terms and Conditions govern the order in which paid visa assistance services are granted when a Visa support request is submitted through IVISA services. 40K. .