Michael Callen (April 11, 1955 - December 27, 1993) was a singer, songwriter, composer, author, and AIDS activist. He was a significant architect of the response to the AIDS crisis in the United States.

First diagnosed with "Gay related immune deficiency" in 1982, Callen quickly became a leader in the response to the epidemic, coining the phrase "people with AIDS (PWAs)" in contrast to the then current "AIDS victims". He was a founding member of the People with AIDS Coalition among other organizations, and he testified before the President's Commission on AIDS and both houses of Congress.

In 1983, he co-authored the book How to Have Sex in an Epidemic: One Approach, which outlined the tenets of safe(r) sex still in use today. In 1990, he wrote Surviving AIDS, which received an Honorable Mention from the American Medical Writers Association.

He was frequently seen on television talking about AIDS. Appearances included Nightline, Good Morning America, 20/20, and The Phil Donahue Show. He wrote for several newspapers and magazines, including the Village Voice, The New York Native, and Outweek; some of his articles are collected in Surviving and Thriving with AIDS, published by the People with AIDS Coalition in 1988.

He was also a well-loved singer and songwriter in the gay community. He founded the gay male a cappella singing group, The Flirtations, with whom he recorded two albums. He also had a solo album, Purple Heart (Significant Other Records, 1988), which a review in The Advocate called, "the most remarkable gay independent release of the past decade." In partnership with Oscar winner Peter Allen and Marsha Melamet, he wrote his most enduring song, "Love Don't Need a Reason," which he sang frequently at gay pride and AIDS-related events around the country.

In 1993 he appeared in the films Philadelphia (as part of The Flirtations) and Zero Patience (as a singing transvestite virus, Miss HIV).

Callen was openly doubtful of the HIV theory of AIDS and especially critical of AZT monotherapy when it was first introduced: "The HIV paradigm has produced nothing of value for my life and I actually believe that treatments based on the arrogant belief that HIV has proven to be the sole and sufficient cause of AIDS has hastened the deaths of many of my friends." (Meditel documentary, 1992)

Callen died of AIDS-related complications in Los Angeles, California, on December 27, 1993. He was 38.