When you file your tax return or need to speak to the IRS, you will likely need to provide a tax identification number, also known as a TIN or tax identification number. Here’s what a tax ID number is and how to apply for it.

A tax identification number (TIN) is a unique nine-digit number that identifies you to the IRS. It is required on your tax return and requested in other interactions with the IRS. Social Security numbers are the most popular tax identification numbers, but four other types are also popular: ITIN, EIN, ATIN, and PTIN.

What it is: An Individual Tax Identification Number (ITIN) is a nine-digit tax identification number for non-resident and resident aliens, their spouses and dependents who cannot obtain a social security number. The IRS issues the ITIN.

How to get an ITIN: To obtain an ITIN, complete IRS Form W-7. You must prove your foreigner / foreigner status and your identity. In addition, you must file a federal income tax return on your W-7 form (there are some exceptions; the W-7 instructions contain the details). Organizations called “acceptance agents” have authorization from the IRS to help people obtain ITINs.

• ITINs always start with the number 9.

• An individual tax ID number with the middle digits 83, 84, 85, 86 or 87 expired at the end of 2019. Individual tax ID numbers with the middle digits 88 expired at the end of 2020.

• ITINs with the middle digits 90, 91, 92, 94, 95, 96, 97, 98 or 99 that were assigned before 2013 and not renewed also expired at the end of 2020.

• Any individual tax identification number not used on a tax return in the past three years has expired at the end of 2020.

What it is: An Employer Identification Number (EIN) is a tax identification number for businesses that have employees; are companies or partnerships; withhold taxes on income paid to non-resident foreigners; have Keogh plans; are involved in certain types of organizations; or file employment, excise or alcohol, tobacco and firearms tax returns. The primary business must be in the United States or a United States territory, and the person applying for the EIN (it must be an individual, not an entity) must already have a Social Security number, an ITIN or other EIN. The IRS may require an estate or trust to obtain an EIN.

How to get an EIN: You can apply for this tax identification number online with IRS. You can also complete IRS Form SS-4 and fax or mail it to the IRS. International applicants can call 1-267-941-1099 to obtain an EIN.

To note: Your business may also need a separate employer identification number.

What it is: An adoption tax identification number (ATIN) is a temporary nine-digit tax identification number that the IRS gives to people who are in the process of adopting a child. The IRS provides the number if the adoptive parents cannot obtain a Social Security number for the child in time to file their tax return. The number identifies the child, not the parent, and is necessary for the parent to claim the child as a dependent.

How to get an ATIN: To obtain an ATIN, deposit IRS Form W-7A. You will need to attach a copy of the investment documentation. The child must be legally placed in your home for adoption. If you adopt a child from another country, you can still get an ATIN, but there are more rules (see details here).

• You cannot claim the income tax credit with this tax ID number (you can only use a social security number to do this).

• It takes four to eight weeks to get an ATIN after the IRS receives your Form W-7A, so ask for it well before your tax return is due.

• Unless you notify the IRS that the adoption is still in progress, the IRS will automatically deactivate an ATIN after two years.

What it is: A PTIN is a preparer tax identification number. The IRS requires that anyone who prepares or helps prepare federal income tax returns for compensation must have a PTIN. Tax preparers must list their PTIN numbers on clients’ tax returns.

How to get a PTIN: Preparers can get PTINs from the IRS online in about 15 minutes. Alternatively, they can complete and mail IRS Form W-12. This method takes about four to six weeks.