On July 28, 2020, the US Internal Revenue Service released over 800 pages of final and new proposed regulations addressing the limits on the deduction for business interest expense contained in Section 163(j) of the Internal Revenue Code. This Code section was completely rewritten in the Tax Cuts and Jobs Act, and the new limits generally apply for tax years beginning in 2018. Partnerships desiring to take advantage of certain transitional rules must act by September 30, 2020, or seek IRS approval for transitional relief. This Legal Update, prepared with the input of numerous members of the Mayer Brown tax department, provides a user-friendly overview of the new rules.