New York Application For Index Number is a form used to apply for a unique identifying number for business entities in New York State. It is used by the Department of State (DOS) to record information about a business and its activities, such as its name, address, purpose, and type of business. The Index Number is also used to identify the business when filing business documents and other paperwork with the DOS. There are three types of New York Application For Index Number: 1) Domestic Business Corporation; 2) Foreign Business Corporation; and 3) Limited Liability Company. Each type has its own form and associated filing requirements.