An LLC or LLP are entities created by state statute. The IRS does not have a tax classification for an LLC or LLP; instead IRS uses the tax entity classifications it has always had for business taxpayers: corporation, partnership, or disregarded as an entity separate from its owner, referred to as a disregarded entity.' If your business is classified by the IRS as a partnership, sole prop or corporation, you can use this checklist (provided by the IRS) to determine whether the new owner needs a new tax ID number: http://www.irs.gov/businesses/small/article/0,,id=98011,00.html