"LMK" is an electro-R&B track which revolves around "a wobbly, three-note synth-bass" with Kelela singing about a "potential one-night-stand." The bass-heavy and industrial production was handled by Jam City. Briana Younger of Pitchfork noted that Jam City's "pristine soundscape, while more minimal than what Kelela usually sings over, complements her well with its blend of space-age clubbiness and sultry R&B. It makes for what is probably her most pop-accessible song to date, an empowered and liberating song that asserts not just a woman's agency, but also Kelela's power as an artist."
"LMK" premiered on Zane Lowe's Beats 1 show on August 1, 2017, and subsequently released for digital download and streaming. Kelela told The Fader that the song is "directed at a man who's being weird instead of being honest. Does casual have to be careless? Is wifey the only woman who deserves your respect, and why do you think I want more when I demand it? These are my questions..."
The music video for "LMK" was uploaded to Kelela's Vevo channel on August 9, 2017. Directed by longtime Björk collaborator Andrew Thomas Huang, the video is "a surreal visual that sees Kelela moving through hazy, club-like environments with authority and a take-no-prisoners attitude." Regarding the video, Huang said: "We wanted make a video that showcases the multiplicity of who Kelela is and who she has the potential to be. The video is essentially a grand unveiling featuring Kelela wearing different wigs and guises as she pushes through the club with her friends, ultimately revealing herself at the end of the video. The message of this video is empowerment: it's for the girls, for anyone whose heart has been trampled on and deserves to go out and feel good about themselves. It's a call to action, demanding to be taken and to be quick about it. This is the reason why we love Kelela - she's making herself vulnerable and kicking down doors in the process."