Under 2017 law, alimony and separate maintenance payments were deductible by the payor spouse and includible in income by the recipient spouse.
Child support payments were not treated as alimony.
Under the new law, alimony and maintenance payments are not deductible by the payor, and are not considered taxable income to the recipient. This will likely result in alimony being taxed to the spouse with the higher tax rate.
Wait, don't panic! This provision applies to divorce/separation agreements executed after December 31, 2018. If you untied the knot before that date, you can stay under the old rule, or, if you like the new law better, you can modify your prior agreement.