On December 21, 2019, the US Internal Revenue Service issued final regulations implementing the qualified opportunity fund rules contained in Section 1400Z-2 of the Internal Revenue Code. The final regulations replace two sets of proposed regulations issued in May and October of 2019. While the final regulations build on and utilize many principles presaged in the proposed regulations, the final regulations make the use of qualified opportunity funds much more user-friendly. The attached Legal Update, prepared by a team of Mayer Brown tax lawyers, summarizes certain of the most salient features of the 550-page regulation package.