The reasons for taxing alimony but not child support are [1] that alimony (in some sense) is not seen as being for the support of family and [2] the government wanted to provide an indirect subsidy to the spouse receiving alimony. Without further explanation, that may seem like a baffling answer... First a word about the full tax treatment of alimony & child support: Although alimony is taxable to the recipient, the payor gets a deduction for it, unlike for the payment of child support. That is, the payor reduces taxable income by paying alimony & the recipient increases taxable income by getting alimony. On the other hand, the payor does not reduce taxable income by paying child support & neither does the recipient increase taxable income. Also, if the spouses so choose, the alimony payments can be tax-exempt to the recipient if the payor will not receive the deduction -- basically treating alimony payments like child support. Reason [1]: Generally the government treats payments between family members in the way it treats child support -- that is, a parent gets no tax break for buying the child a pair of sneakers (nor does the child have "income" from the gift); likewise, a spouse does not get a tax break for "putting food on the table" (nor does the other spouse have to include the food in income). So, child support is seen simply as a fulfillment of a family obligation, deserving of no tax deduction or inclusion in anyone's income. Alimony on the other hand, in some respects, is not seen as support of family, but more like a business transaction between unrelated parties. But this first reason doesn't adequately explain the ability of the spouses to choose to have alimony payments treated like child support payments. Reason [2]: The government is providing an indirect subsidy to the spouse receiving alimony. It may seem strange to provide a subsidy to the spouse receiving alimony by making it taxable, rather than tax-exempt income, but I assure you it is true. Consider this: The spouse paying alimony has $154 of income and is taxed at a rate of 35%. If the spouse does not receive a deduction, the $154 will incur $54 of tax (35% of $154), leaving $100 which is paid as alimony and leaving $0 in the spouse's pocket. On the other hand, if the spouse is given a deduction, the spouse can pay $154 in alimony, deduct the payment form the $154 of income, leaving $0 of taxable income, $0 of tax, and the same $0 in the spouse's pocket. A spouse in the 35% tax bracket paying alimony is indifferent between [a] paying $100 without a deduction or [b] paying $154 with a deduction. (Remember that the spouses can essentially choose between [a] and [b]. [b] is the typical rule and [a] is the elective rule.) Now consider the spouse receiving the alimony -- If (and only if) the spouse receiving alimony is in a lower tax bracket, then the recipient would rather pay tax on the alimony than not. [a] If the spouse receives $100 of tax-exempt alimony, no tax is owed, leaving $100 in the recipient's pocket. [b] However, if the spouse is taxed at 28% on the $154 of taxable alimony, the total tax is $43, leaving $111 dollars in the recipient's pocket. [Note that if the tax rate is 15% the recipient will have $131 and if the tax rate is 35% (i.e. same as the payor) the recipient will have only $100 after taxes.] So, as long as the recipient spouse is in a lower tax bracket than the payor spouse, the recipient would prefer to be under the [b], typical alimony rule, providing a deduction for the payor and taxable income to the recipient. The extra money in the recipient's pocket is money that the government is not collecting as tax. That is, under [a] the government collects $54 of tax, all from the payor; under [b] the government collects only $43 of tax, all from the recipient. Since the recipient of alimony is usually in a lower tax bracket than the payor of the alimony, the typical rule usually provides a subsidy. If the recipient and payor are in the same tax bracket, neither cares (in net tax terms) whether the typical or elective rule applies. If the recipient is in a higher tax bracket than the payor, the payor still is indifferent, but the recipient would rather elect the no-deduction / tax-exempt rule. In the alimony / child support negotiations during a divorce, a good lawyer ought to use the alimony deduction and as a bargaining chip. It is important that the payor realize that $100 of child support is not the same as $100 of alimony -- $100 of child support (with no deduction) is the same as $154 of alimony (with a deduction from 35% taxed income). Also, be careful about whether the divorce agreement elects to have the alimony payments treated under the no-deduction / tax-exempt rule, because it very significantly affects the net-of-tax incomes.