Yaoi comics became popular in the 1970s as a specific type of donjinshi (self-published work). The first Yaoi published was titled "June".
The name Yaoi comes from the Japanese expression "yama nashi, ochi nashi, imi nashi" which means "no climax, no punchline, no meaning," which encompasses the liberating message of Yaoi-style comics.
Bara comics are different from Yaoi books; that's because Bara comics are created for gay men by gay men. Yaoi books specifically target female audiences. Yuri comics, however, target lesbian readers.
According to Yaoi 911, Yaoi books are becoming increasingly popular in the United States; they are sold by big distributors like Amazon.com. The first American Yaoi was "Sexual Espionage #1" by Daria McGrain.
Yaoi comics do receive their fair share of controversy. Some of the material is considered pornographic, and a fair amount of people attack and criticize this form of literature.