Wisconsin IRS Form W9 is an information document used by the Internal Revenue Service (IRS) to collect tax information from Wisconsin residents. It is used by the IRS to obtain an individual's name, address, Social Security Number (SSN) or Taxpayer Identification Number (TIN), or an Employer Identification Number (EIN) if applicable. It is also used by businesses, organizations, and other entities to obtain the same information for the purpose of reporting income. There are two main types of Wisconsin IRS Form W9: Form W-9 for individuals and Form W-9S for businesses.