The Business Number is a number you are assigned when you do any business with the Canada Revenue Agency (CRA), such as registering for the GST/HST or filing corporate income tax.
This single Business Number replaces the numbers that Canadian businesses previously needed to deal with the federal government. If you had accounts with the Canada Revenue Agency before the Business Number came into effect, your GST/HST number became your Business Number.
The Business Number includes four common CRA accounts; corporate income tax; import/export; payroll deductions; and the goods and services tax/harmonized sales tax (GST/HST).
Note that your small business may not need a business number.
If your small business does not need any of the tax accounts listed above (i.e. your small business is a Small Supplier in terms of the GST/HST, which means you don't have to register for GST/HST), then your small business doesn't have to have a Business Number.
If your small business does need a Business Number, you can register for the Business Number by phone, by fax, by mail, via the Internet, or in person. The Canada Revenue Agency form you need to register for the Business Number is RC1, Request for a Business Number.
Note that "If your business is in Quebec, the Business Number does not include your GST/HST accounts. The Ministère du Revenu du Québec (MRQ) administers GST/HST for the CRA. If you plan to register only for the GST/HST in Quebec, you do not need to complete Form RC1 Request for a Business Number" (The Business Number and Your CRA Accounts). For more information, see the Canada Revenue Agency page Operating in Quebec.