"U Know What's Up" is a 1999 hit song by singer-songwriter-producer Donell Jones' second studio album, Where I Wanna Be. The song features Lisa Lopes of TLC. It reached number one on the Billboard Hot R&B/Hip-Hop Singles & Tracks chart on November 13, 1999, and stayed at number one for eight consecutive weeks. It peaked at number seven on the Billboard Hot 100, remaining there for two consecutive weeks. Outside the United States, the song peaked within the top ten of the charts in the United Kingdom. The song was produced by Edward "Eddie F" Ferrell and Darren Lighty for Untouchables Entertainment. It is Jones's biggest hit to date. The song was co-written by Anthony Hamilton.

There is a remix also produced by Donell Jones and features new verses by Jones and verses by rappers on a new urban beat. There is also a radio version that excludes Left Eyes rap bridge, catered to Adult R&B formats.

The video features rapper Lisa Lopes of TLC, YoungBloodZ, T.I., Usher (Jones' childhood friend) and Big Boi of OutKast, all of whom were (including Jones) part of the LaFace Records label. At the beginning of the video, there is a sign that says La Face Place, in reference to the record label.

The video begins with Lisa Lopes at her apartment receiving a phone call, presumably from Jones, informing her that the music video for the song is being aired on TV. She turns to the TV screen behind her playing the video, which shows Jones at a hotel party, and proceeds to watch it. As it turns out, Lopes is not the only person watching the video, as the video pans across the building showing Usher and his girlfriend at his apartment, and Big Boi hosting a music video premiere at his apartment. Midway through the video, Lopes leaves her apartment and recites her verse in the song while walking across the corridor, presumably to join Jones at a similar party at the back of the building, which is revealed as the camera pulls back from the corridor. At the end, the video pulls back to reveal Jones watching it at his apartment with his girlfriend.

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