"Ain't It Funny (Murder Remix)" is a song by American singer Jennifer Lopez, featuring American rappers Ja Rule and Caddillac Tah. Written by Lopez, Cory Rooney, Ja Rule, Caddillac Tah, Ashanti, and 7 Aurelius, it was released in 2002 as the lead single from Lopez's remix album, J to tha L-O!: The Remixes(2002). The song was also included on the 2002 compilation album Irv Gotti Presents: The Inc.as well as on Ja Rule's greatest hits album Exodus.

The single topped the U.S. Hot 100 becoming Lopez's third number-one single and Ja Rule's third number-one single; it also peaked at number four in the United Kingdom. Caddillac Tah also performs on the song and appears on the song's music video, and even has a longer part than Ja Rule. The remix samples Craig Mack's 1994 hit "Flava in Ya Ear". The song spent six weeks at the top of the BillboardHot 100 from March 9, and followed another Ja Rule duet, "Always on Time" with Ashanti. Ashanti's "Foolish" replaced it at the number-one spot. Ashanti also appears in the video alongside Lopez, Ja Rule, Irv Gotti, Caddillac Tah, and other Inc. members.

The original version of the song, "Ain't It Funny", appears on Lopez's second studio album, 2001's J.Lo, and was also a single of its own. It was written by Cory Rooney for the soundtrack to Lopez's film The Wedding Planner, but it was felt that the timbales gave it too much of a Latin sound, and the song was not used for the soundtrack. After the success of "I'm Real (Murder Remix)", a previous Lopez–Ja Rule collaboration, they decided to remix "Ain't It Funny" as a duet and release it as a follow-up. Unlike "I'm Real", the two versions of "Ain't It Funny" were released on different dates, and so charted separately. The songs also charted separately because Billboardinstituted a new chart policy.

In the Murder Inc. studio then-upcoming artist Ashanti dropped by the studio. "Everyone was there and Ja (Rule) was on the floor playing video games, and they had the beat playing in the background. Chris Gotti, Irv Gotti's brother, said 'Ja's supposed to be writing this record for J-Lo, but it doesn't look like he's going to be doing anything tonight. Why don't you go in there and see what's happening?' So that's exactly what I did", says Ashanti, who wrote two verses and demoed the new "Ain't It Funny" for Lopez. Ashanti recalled, "I got a call from Gotti in Los Angeles. He asked me to write another verse[...] I had to write it over the phone and two-way Irv the lyrics."

The video is in two parts which frequently interchange back and forth throughout the song. The first part of the video shows Lopez having a small party in her home with guests including Ja Rule and Ashanti. This part of the video is from the point of view of the guy who is being mentioned in the song. His face is not seen, and Lopez addresses the camera throughout this section of the video. This section begins with the guy knocking on the door, Lopez inviting him in, and then eventually showing him the door when she sees him attempting to look/flirt with other women at the party. As he leaves, she goes on entertaining the other guests.

The second part of the video involves scenes with Lopez and Ja Rule in a white room, Ja Rule in a recording studio in Lopez's home, Lopez sitting in a chair singing bits of the song, and Lopez and Ja Rule singing the parts of the final verse against a gold backdrop.