On Bullshit is an essay by philosopher Harry Frankfurt. Originally published in the journal Raritan in 1986, the essay was republished as a separate volume in 2005 and became a nonfiction bestseller, spending twenty-seven weeks on the New York Times Best Seller list.[1]

In the essay, Frankfurt defines a theory of bullshit, defining the concept and analyzing its applications. In particular, Frankfurt distinguishes bullshitting from lying: while the liar deliberately makes false claims, the bullshitter is simply uninterested in the truth. Bullshitters aim primarily to impress and persuade their audiences. While liars need to know the truth to better conceal it, bullshitters, interested solely in advancing their own agendas, have no use for the truth. Thus, Frankfurt claims, "...bullshit is a greater enemy of the truth than lies are," (Frankfurt 61).

This work laid the foundation for Frankfurt's 2006 follow-up book, On Truth.