From Pub 590:
Can you contribute to a Roth IRA for your spouse? You can contribute to a Roth IRA for your spouse provided the contributions satisfy the Kay Bailey Hutchison Spousal IRA limit discussed in chapter 1 under How Much Can Be Contributed, you file jointly, and your modified AGI is less than $188,000.
Kay Bailey Hutchison Spousal IRA Limit
For 2013, if you file a joint return and your taxable compensation is less than that of your spouse, the most that can be contributed for the year to your IRA is the smaller of the following two amounts:
$5,500 ($6,500 if you are age 50 or older), or
The total compensation includible in the gross income of both you and your spouse for the year, reduced by the following two amounts.
Your spouse's IRA contribution for the year to a traditional IRA.
Any contributions for the year to a Roth IRA on behalf of your spouse.
This means that the total combined contributions that can be made for the year to your IRA and your spouse's IRA can be as much as $11,000 ($12,000 if only one of you is age 50 or older or $13,000 if both of you are age 50 or olde