"I'm So Glad" is a song originally recorded by Skip James in 1931. The song is derived from a song written in 1927 by Art Sizemore and George A. Little entitled "So Tired" and first recorded that same year by Curley Huber. It was covered by Cream on their first album,Fresh Cream, then later put on their last studio album Goodbye as a live performance. It was also covered by Deep Purple on their first album Shades of Deep Purple and by Yuya Uchida and the Flowers on their debut album Challenge. Their version is introduced by their own arrangement called "Prelude: Happiness". The Skip James-song itself starts after a medley consisting of excerpts from the instrumental arrangement of Rimsky-Korsakov's classical Scheherezade. This medley named "Prelude: Happiness", stretches the song over the 7 minute mark.
The band decided to record the song after vocalist Rod Evans and drummer Ian Paice had recommended it. Evans and Paice had previously, (around the mid-sixties), played in a band together, called The Maze. The Maze had also recorded "I'm So Glad", which Evans and Paice both thought had potential for a song that Deep Purple could succeed commercially with.
Deep Purple supported Cream on their Farewell Tour in October 1968 where Cream's Goodbye version was recorded, and recorded their own live album, entitled Inglewood - Live in California on the same night. This album is the only live-recording by Deep Purple's earliest line-up, Mark 1, released on an album, besides very rare bootlegs. The album was shelved by the label in 1968, but it was finally released in 2002, after 34 years away from public.