Feminization or feminisation, sometimes forced feminization (shortened to forcefem or forced femme), and also known as sissification, is a practice in dominance and submission or kink subcultures, involving reversal of gender roles and making a submissive male take on a feminine role, which includes cross-dressing. Subsets of the practice include "sissy training" and variations thereof, where the submissive male is "trained" to become feminine.

Feminization as a sexual fetish is not the same thing as being a transgender woman, and the submissive partners engaging in it are typically cisgender men. It has been speculated that the fetish is rooted in societal pressure for men to be traditionally masculine.

Feminization is a practice in dominance and submission or kink subcultures, which involves reversing gender roles, making a submissive partner – typically a man – take on a feminine role, often for humiliation-based sexual pleasure. This may include them cross-dressing in feminine clothing such as lingerie, makeup, jewellery, perfume, acting in a feminine manner, getting referred to by a feminine name, having anal sex as the receptive partner, wearing prosthetic breasts, or tucking.

People participating in feminization often role-play different scenarios based around the submissive partner's femininity or feminine clothes; these may include role-playing being caught in the act of trying on panties or lipstick, being discovered to be wearing frilly lingerie under their clothes, being a princess, being a "damsel in distress" and treated like a helpless woman, or being hired "as a woman" for a female-coded job like a nurse, cheerleader, sex worker, or businesswoman. HuffPost described one dominatrix's sissification sessions as involving humiliating the submissive by "parading them around" in high heels, make-up, and lingerie; another dominatrix does her sessions by "cheerleading" men into exploring femininity.

Despite being labeled as "forced" feminization, as the role-played scenario may involve that the submissive partner supposedly is feminized against their will, it is a fantasy that is agreed upon by its participants. Whereas not all participants are interested in BDSM aspects of the practice, and only enjoy dressing up, it may also include things such as spanking, pegging, bondage, and humiliation such as making fun of the submissive for having a small and soft penis, and referring to it as a clitoris. The feminized partner is sometimes called a "sissy", and may be said to have been "sissified".

A subset of feminization is "sissy training", wherein the dominant partner slowly over time trains the submissive in being a sissy, making them take on "ultra-feminine" behaviors and participate in feminine activities. As part of this, it is common for the sissy to cross-dress; to shave their body, including their genitals; wear make-up; and wear women's underwear, to appear more womanly. Activities in sissy training involve non-sexual ones, such as applying make-up or cleaning the house, as well as sexual ones.

A further subset is "sissy maid training", a common scenario, where the sissy takes on the role of a maid, taking care of housework or serving drinks and food at a party while behaving submissively and wearing an often frilly and revealing maid uniform, such as a French maid or rubber maid dress. The dominant partner in a sissy maid training scenario, overseeing the sissy's housework, may role-play punishing them with things such as spanking, humiliation or bondage, whether the infraction was real or made up; a reward for good behavior might be allowing the submissive to orgasm.

Another common sub-set is "slut training", where the submissive partner is made to wear "slutty" feminine clothing that may reveal a lot of bare skin and show off the submissive's curves, while being teased or chided for being promiscuous or overly sexual. The training involves making the submissive – who often may be shy and embarrassed – overcome those emotions, shifting their mindset so that they instinctively act more provocatively and uninhibitedly. The training may include training the submissive to pose provocatively, such as spreading their buttocks or exposing their genitals, and making them instinctively assume certain such positions in certain situations.