The expression junk science is used to describe scientific data, research, or analysis considered by the person using the phrase to be spurious or fraudulent. The concept is often invoked in political and legal contexts where facts and scientific results have a great amount of weight in making a determination. It usually conveys a pejorative connotation that the research has been untowardly driven by political, ideological, financial, or otherwise unscientific motives.

The concept was popularized in the 1990s in relation to expert testimony in civil litigation. More recently, invoking the concept has been a tactic to criticize research on the harmful environmental or public health effects of corporate activities, and occasionally in response to such criticism. Author Dan Agin in his book Junk Science harshly criticized those who deny the basic premise of global warming,

In some contexts, junk science is counterposed to the "sound science" or "solid science" that favors one's own point of view. Junk science has been criticized for undermining public trust in real science.^{: 110–111}