Section 152(e) of the tax code speciﬁes how to determine the dependent status of children of divorced parents. This code section states that the noncustodial parent can claim the dependency exemption for a child when the custodial parent signs a written
declaration that the custodial parent will not claim such child as a dependent for any taxable year beginning on the date of such taxable year. I always recommend doing this using IRS Form 8332.
According to Leslie Himes, et ux., v. Commissioner TC Memo 2010-97 when a custodial parent does not release the dependency exemption, the custodial parent is deemed to be the taxpayer who is entitled to claim the exemption for the child.