The IRS tax law specifically states that "if you are divorced or separated, you may be able to deduct the alimony or separate maintenance payments that you are required to make to your spouse or former spouse, or on behalf of that spouse."
The deduction is taken only on Form 1040 (long form only) and shown as an adjustment to your income on Line 31a. The IRS requires the Social Security Number for the spouse receiving the Alimony.
The code section defines Alimony as a "payment to or for a spouse or former spouse under a divorce or separation instrument
. The code sections specially excludes voluntary payments
that are not made under a divorce or separation instrument.
For more details, please refer to IRS Publication 504. Please click on IRS link below to get more detailed discussion on this subject. Publication 504 (2006), Divorced or Separated Individuals