Treasury released new final regulations under sections 334(b)(1)(B) and 362(e)(1) of the Internal Revenue Code of 1986 (Code) that deal with loss importation. Very generally, these rules relate to property that has a built-in loss that is transferred from non-US entities to US persons. The basic premise is that losses accrued outside the US should not shelter US income.
The effective date of the rules is March 26, 2016 with certain exceptions.
A couple of articles that address these rules in a bit more detail: