What was the name of Janis Joplin's backing band at Woodstock?

Janis Joplin’s backing band at Woodstock was the Kozmic Blues Band.

Joplin had separated from Big Brother and the Holding Company, the San Francisco group that had helped make her famous, and formed a new ensemble in 1969. The Kozmic Blues Band combined session musicians, a horn section, and several players connected with her earlier circle, including guitarist Sam Andrew and bassist Brad Campbell.

Joplin performed at Woodstock at approximately 2 a.m. on August 17, 1969. Her set included songs such as “Try (Just a Little Bit Harder),” “To Love Somebody,” and “Piece of My Heart,” along with her celebrated performance of “Ball and Chain.” She was reportedly dissatisfied with the performance, so it was omitted from the original 1970 documentary and soundtrack; footage was later included in an anniversary director’s cut.

The main source of confusion is Full Tilt Boogie Band, which became Joplin’s backing group later, in 1970. Big Brother and the Holding Company was her earlier band, not the group backing her at Woodstock.