"Didn't I (Blow Your Mind This Time)" is a song by American soul group the Delfonics, co-written by producer Thom Bell and lead singer William Hart. It was released as a single in 1969 on the Philly Groove record label and appeared on their self-titled third album the following year. The song reached number three on the Billboard R&B chart and number ten on the Billboard Hot 100 in 1970.^[3] Overseas, the song peaked at number 22 on the UK Singles Chart in and number 81 in Australia.^[4][5] The Delfonics won a Grammy Award for Best R&B Vocal Performance by a Duo or Group for the song in 1971.

A prominent example of the Philadelphia soul style, "Didn't I" is a slow ballad, with layered strings and horns and highly chromatic harmony.

A version by boy band New Kids on the Block, slightly re-titled "Didn't I (Blow Your Mind)", was featured on the group's 1986 self-titled debut album. Their version was later released as a single in 1989 in an attempt to boost sales of its parent album in light of the group's subsequent success. The single peaked at number eight on both the US and UK pop charts, peaking in November 1989 in the US and in October of the following year in the UK (as a double A-side alongside "Let's Try It Again").

The song has been extensively covered since 1970, by artists included Aretha Franklin (from Young, Gifted and Black in 1971), brothers David and Jimmy Ruffin, Spinners (from Can't Shake This Feeling in 1981), Lisa Fischer, Regina Belle, Jackie Jackson, the Trammps, Maxine Nightingale and Patti LaBelle.

Millie Jackson's version peaked number 49 in the Billboard Hot R&B/Hip-Hop Songs chart in March 1980.^[19]

Philadelphia-era natives Daryl Hall and Todd Rundgren covered the song on Episode 40 of Live From Daryl's House.^{[citation needed]}