"The Greatest" is a song recorded by Australian recording artist Sia for the deluxe edition of her seventh studio album, This Is Acting (2016). Being made available for digital consumption as the record's third single on September 5th, 2016 through Monkey Puzzle and RCA Records, "The Greatest" features the vocal collaboration of American rapper Kendrick Lamar. The electropop and tropical house song was written by Sia, Greg Kurstin, and Lamar while production was solely handled by Kurstin. The solo version was written solely by the latter two.

An accompanying music video for the single was filmed by Sia and Daniel Askill, and portrays American dancer Maddie Ziegler among 48 others. Although the singer has not provided an interpretation of the video's plot, numerous media outlets have perceived it as a tribute to the 49 victims of the 2016 Orlando nightclub shooting. Commercially, "The Greatest" reached the top five in several countries and was awarded with certifications in various territories.

Billboard editor Gil Kaufman described "The Greatest" as a "uplifting, poppy song with a subtle island vibe."

The song is written in the key of C minor with a cut common time tempo of 96 beats per minute. The vocals span from B♭₃ to E♭₅ in the song.

Jessica Goodman from Entertainment Weekly found the chorus "massive and catchy." Once the critics had picked up on the song's connection with the 2016 Orlando nightclub shooting, Spencer Kornhaber of The Atlantic wrote:

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