"I'll Feel a Whole Lot Better" is a song by the Los Angeles folk rock band The Byrds that was first released in June 1965 on the B-side of the band's second single, "All I Really Want to Do". It was also included on The Byrds' debut album, Mr. Tambourine Man. Written by Gene Clark, who also sings the lead vocal, "I'll Feel a Whole Lot Better" features some of The Byrds' early musical trademarks, including Jim McGuinn's jangling 12-string Rickenbacker guitar; Clark's pounding tambourine; McGuinn, Clark and David Crosby's complex harmony singing; and a country-influenced guitar solo.