Fringe science is scientific inquiry in an established field of study which departs significantly from mainstream or orthodox theories, and is classified in the "fringes" of a credible mainstream academic discipline. Mainstream scientists typically regard fringe concepts as highly speculative or strongly refuted, as opposed to frontier science which is plausible emerging science.

Though there are examples of mainstream scientists supporting maverick ideas within their own discipline of expertise, fringe science theories and ideas are often advanced by individuals either without a traditional academic science background, or by researchers outside the mainstream discipline, although history of science shows that scientific progress is often marked by interdisciplinary and multicultural interaction. Friedlander suggests that fringe science is necessary for mainstream science "not to atrophy", as scientists must evaluate the plausibility of each new fringe claim and certain fringe discoveries "will later graduate into the ranks of accepted" while others "will never receive confirmation". The general public has difficulty distinguishing between "science and its imitators", and in some cases a "yearning to believe or a generalized suspicion of experts is a very potent incentive to accepting pseudoscientific claims".

The term fringe science is sometimes loosely used to describe fields which are actually pseudosciences, or fields which are referred to as sciences, but entirely lack scientific rigor or plausibility. Scientists have coined the terms pathological science, voodoo science and cargo cult science to describe inquiry lacking in scientific integrity. Junk science is typically used politically to describe agenda-driven science. Fringe science, in contrast, does have some degree of scientific rigor, plausibility, and integrity, though it is usually highly disputed. Fringe science is sometimes also referred to as questionable science.