To file jointly, you must elect to treat your wife as a US person for income tax purposes. The forms you need to file are listed in @Critter-3 's answer.
If you elect to treat your wife as a US person for income tax purposes, you must report all your wife's world-wide income on your joint US tax return and pay US tax on it. (If you file separately, you only report your own income.) If your wife also pays foreign income tax, you can claim a deduction or credit on your joint return for those foreign taxes, but the final result may be that you pay more US tax than you would otherwise. The only way to know for sure is to prepare test tax returns for your exact circumstances.
Failing to declare and pay US tax on your wife's world-wide income (if you file jointly) could affect her immigration status if she applies for residency.
