"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. Overseas, the song peaked at number 22 on the UK Singles Chart in and number 81 in Australia. The Delfonics won a Grammy Award for Best R&B Vocal Performance by a Duo or Group for the song in 1971.

The Delfonics were an American R&B/soul vocal group from Philadelphia. The Delfonics were most popular in the late 1960s and early 1970s. Their most notable hits include "La-La ", "Didn't I ", "Break Your Promise", "I'm Sorry", and "Ready or Not Here I Come ". Their hit songs were primarily written by lead vocalist and founding member William "Poogie" Hart, and arranger and producer Thom Bell. Wilbert Hart is the last surviving founding member.