EIN or Employer Identification Number is a mandatory and important nine digit number assigned to business entities by the IRS. It is also known as Federal Tax Identification. The Internal Revenue Service IRS uses this number to identify business entities that are required to file different tax returns and not intended for use in any other activity like lotteries. In most cases, businesses require EIN when their organization structure has changed or after a change of ownership. The number is used by employers, corporations, partnerships, non-profit making organizations, government agencies, trusts and estates. There are various ways to obtain the number including online application.