If you want to file a joint return and he doesn't have a social security number, he will need to apply for and receive a taxpayer identifying number.
You can file married filing jointly or married filing separately. If the latter and your spouse has no US source income, he/she would not be required to file.
The following is from the IRS regarding married filing jointly:
If, at the end of your tax year, you are married and one spouse is a U.S. citizen or a resident alien and the other is a nonresident alien, you can choose to treat the nonresident as a U.S. resident. This includes situations in which one of you is a nonresident alien at the beginning of the tax year, but a resident alien at the end of the year, and the other is a nonresident alien at the end of the year.
If you make this choice, the following two rules apply:
--- You and your spouse are treated, for income tax purposes, as residents for all tax years that the choice is in effect
--- You must file a joint income tax return for the year you make the choice
If you make this choice, you and your spouse are treated as residents for your entire tax year for the purpose of your federal individual income tax return, and for the purpose of withholding U.S. federal income tax from your wages.
Generally, neither you nor your spouse can claim tax treaty benefits as a resident of a foreign country for a tax year for which the choice is in effect and you are both taxed on worldwide income. However, the exception to the saving clause of a particular tax treaty might allow a resident alien to claim a tax treaty benefit on certain specified income. You must file a joint income tax return for the year you make the choice, but you and your spouse can file joint or separate returns in later years.
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Making the Election
You make the choice by attaching a statement, signed by both spouses, to your joint return for the first tax year for which the choice applies. It should contain the following:
--- A declaration that one spouse was a nonresident alien and the other spouse a U.S. citizen or resident alien on the last day of your tax year, and that you choose to be treated as US residents for the entire tax year, and
--- The name, address, and social security number (or individual taxpayer identification number) of each spouse. (If one spouse died, include the name and address of the person making the choice for the deceased spouse.)
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SSN or ITIN
If your spouse is a nonresident alien and you file a joint, your spouse must have either a Social Security Number (SSN) or an Individual Taxpayer Identification Number (ITIN). To get an SSN for your spouse, apply at a social security office or US consulate. You must complete Form SS-5. You must also provide original or certified copies of documents to verify your spouse's age, identity, and citizenship. If your spouse is not eligible to get an SSN, he or she can file Form W-7 with the IRS to apply for an ITIN. Refer to Taxpayer Identification Numbers (TIN) for more information.
