Klein published "The Bisexual Option: A Concept of One Hundred Percent Intimacy " in 1978, based on his research, the world's first real psychological study of bisexuality. He also co-authored "The Male, His Body, His Sex" in 1978. Klein moved to San Diego in 1982. He published "Bisexualities: Theory and Research" in 1986. In 1998 he founded the American Institute of Bisexuality (AIB), also known as the Bisexual Foundation or the Bi Foundation, to encourage, support and assist research and education about bisexuality. Klein also founded the "Journal of Bisexuality". He remained the Journal's principal editor until his death. He published "Bisexual and Gay Husbands: Their Stories, Their Words" in 2001. Klein published a novel, "Life, Sex and the Pursuit of Happiness" in 2005.