The facial feedback hypothesis, rooted in the conjectures of Charles Darwin and William James, is that one's facial expression directly affects their emotional experience. Specifically, physiological activation of the facial regions associated with certain emotions holds a direct effect on the elicitation of such emotional states, and the lack of or inhibition of facial activation will result in the suppression (or absence altogether) of corresponding emotional states.

Variations of the facial feedback hypothesis differ in regards to what extent of engaging in a given facial expression plays in the modulation of affective experience. Particularly, a "strong" version (facial feedback is the decisive factor in whether emotional perception occurs or not) and a "weak" version (facial expression plays a limited role in influencing affect). While a plethora of research exists on the facial feedback hypothesis and its variations, only the weak version has received substantial support, thus it is widely suggested that facial expression likely holds a minor facilitative impact on emotional experience. However, a 2019 meta-analysis, which generally confirmed small but significant effects, found larger effect sizes in the absence of emotional stimuli, suggesting that facial feedback has a stronger initiating effect rather than a modulating one.

Further evidence showed that facial feedback is not essential to the onset of affective states. This is reflected in studies investigating emotional experience in facial paralysis patients when compared to participants without the condition. Results of these studies commonly found that emotional experiences did not significantly differ in the unavoidable absence of facial expression within facial paralysis patients.

Charles Darwin was among the first to suggest that physiological changes caused by an emotion had a direct impact on, rather than being just the consequence of that emotion. He wrote:

The free expression by outward signs of an emotion intensifies it. On the other hand, the repression, as far as this is possible, of all outward signs softens our emotions... Even the simulation of an emotion tends to arouse it in our minds.

Succeeding this postulation, William James (who was also a principal contributor to the related James-Lange theory) proposed that instead of the common belief an emotional state results in muscular expression, proprioception activated by a stimulus "is the emotion" and should one "refuse to express a passion...it dies". In other words, in the absence of awareness of bodily movement, there is only intellectual thought, with consequently the mind being devoid of emotional warmth.

During this period, the posits culminating in the facial feedback hypothesis lacked evidence, apart from limited research in animal behavior and studies of people with severely impaired emotional functioning. Formalized research on Darwin's and James' proposals were not commonly conducted until the latter half of the 1970s and the 1980s; almost a century after Darwin's first proposal on the topic. Furthermore, the term "facial feedback hypothesis" was not popularized in research until around 1980, with one early definition of the hypothesis being "skeletal muscle feedback from facial expressions plays a causal role in regulating emotional experience and behaviour."

While James included the influence of all bodily changes on the creation of an emotion, "including among them visceral, muscular, and cutaneous effects", modern research mainly focuses on the effects of facial muscular activity. One of the first to do so, Silvan Tomkins wrote in 1962 that "the face expresses affect, both to others and the self, via feedback, which is more rapid and more complex than any stimulation of which the slower moving visceral organs are capable".