Eilish and her brother Finneas O'Connell wrote most of the material on the EP and were solely responsible for its production.

The song was certified gold in the United States by the Recording Industry Association of America (RIAA).

In July 2017, Eilish told Billboard that "each track off Don't Smile at Me will follow a distinct plot".

[8] The following track, "Idontwannabeyouanymore", is a pop and R&B song, with a jazz and neo soul-influenced melody.

[12] According to Baeble Music's Olivia Lewis, "My Boy" begins with a "chiller, jazz-like vibe, and a layer of darkness and mystery".

[13] With "Watch", described as a pop ballad,[9][15] Eilish sends a message to her former lover, saying she is leaving their toxic relationship.

[14] "Bellyache" is a mid-tempo electropop and R&B song[17][18] with influences of hip hop, deep house and Latin macabre in its instrumentation.

[19][20][21] The song's lyrics were written from the perspective of a psychopath who kills those close to her, including her friends and lover.

[34][35] The track features minimalist production consisting of a piano, violin strings provided by Madison Leinster, and percussion,[35][36] as Eilish and Khalid sing about the feeling of being trapped inside of one's own mind.

[38] Lyrically, the song delves into the aftermath of a breakup, with Eilish pretending she no longer needs or cares about her former lover.

[43][44] The Australian Recording Industry Association (ARIA) certified the song quadruple platinum in Australia.

[45] The song spawned two music videos; Megan Thompson directed the first released on March 24, 2016.

[64] "&Burn", featuring American rapper Vince Staples, was released as a single on December 15, 2017 and later included on the EP's reissue.

[66] "Party Favor" was released on an exclusive pink 7-inch vinyl as the seventh and final single from Don't Smile at Me on April 21, 2018, coinciding with that year's Record Store Day.

A cover of "Hotline Bling", originally performed and written by Canadian rapper Drake, was released as the B-side.

[68] "Lovely", featuring Khalid, was released as the lead single for 13 Reasons Why: Season 2 (Music from the Original TV Series) on April 19, 2018,[69] and later included on the expanded edition of the EP.

[79] She added the performance was "the type of show where you are acutely aware that the artist you are currently watching will outgrow the venue they are playing almost immediately".

[79] The staff of The Gazette felt Eilish "wants to bring the audience into her world, creating an experience for them".

Kristin Smith of Plugged In said of the EP, "A fusion of multiple genres, sounds and styles, these nine tracks capture the young singer's undeniably engaging perspective and personality.

"[84] Nicole Almeida of Atwood Magazine wrote Don't Smile at Me was a "powerful declaration", and a "statement coming from the mouth of someone who knows who she is.

"[9] Robert Christgau, writing for Vice, commended Eilish's "still-fragile melodies and still-pure voice" on the EP, but considered the songwriting and production to be less accomplished than that of her debut single When We All Fall Asleep, Where Do We Go?.

[83] Tom Hull mentioned that Don't Smile at Me's singles are "more pop", and more "easily distinguished from the filler".

[82] Brenton Blanchet of Spin magazine lauded the EP, saying it was the "first sample of what Eilish could create in her bedroom", saying the "airy and atmospheric project showcased pop craft beyond her age".

[85] Don't Smile at Me became a sleeper hit in the US, debuting at number 185 on the US Billboard 200 a month and a half after its release.

[87] Don't Smile at Me reached the top 40 of the Billboard 200 in the week ending July 28 at number 38 with 12,000 units, including 10,000 streaming equivalent album units,[87] before peaking at number 14 in its 56th charting week for the issue dated January 26, 2019.

[88] As of April 2019, the EP has sold 947,000 album-equivalent units in the US and has also generated more than 1.2 billion on-demand audio streams for its tracks.

[92] In early 2019, Eilish became the youngest artist to hit one billion streams on Spotify with Don't Smile at Me.