Bobby-Soxer is a slang term and youth subculture that described adolescent girls, typically aged 12 to 17, in the United States during the mid-to-late 1940s. The name, which was imposed by the media rather than self-applied, derived from the girls' signature fashion of short, white ankle socks worn folded down with loafers or saddle shoes.

The subculture was characterized by zealous fandom for traditional popular music (especially the crooning of Frank Sinatra) and pioneering a new, peer-oriented casual youth aesthetic that emphasized conformity and emotional expression. The Bobby-Soxer phenomenon signaled a crucial shift in American society, establishing teenagers as a major distinct consumer demographic.

They are often retrospectively considered a "patient zero" for intense modern fandom, with their devotion to Frank Sinatra drawing contemporary comparisons to later phenomena such as 1960s Beatlemania and the "Swifties" fandom surrounding Taylor Swift.

The Bobby-Soxer phenomenon emerged during the cultural disruptions of World War II and the subsequent post-war economic boom. The subculture gained visibility around 1943. The iconic bobby socks themselves gained popularity out of necessity and rebellion: wartime restrictions and the diversion of materials like nylon and silk to military production made full-length stockings scarce, prompting girls to adopt the shorter, folded cotton ankle socks. This new casual style, often paired with saddle shoes or loafers, diverged sharply from the formal attire of previous generations.

Frank Sinatra's solo career coincided perfectly with this rise. His intimate vocal style proved highly popular with adolescent girls, creating an emotional outlet amid wartime uncertainties. Sinatra's 1942 performance at the Paramount Theatre in New York City set the template for mass teen idol worship, marked by intense physical and emotional reactions from his female fans.

The presence of Bobby-Soxers signaled the emergence of a lucrative youth consumer market. Advertisers and businesses, recognizing the immense spending power of these "teen tycoons," began targeting products specifically at adolescent girls, prolonging the period of adolescence. This market was sustained by the girls' own income from part-time jobs and allowances, which they spent on entertainment, fashion, and records.

The intense, often hysterical, fandom demonstrated by Bobby-Soxers—who engaged in public swooning (dramatic groaning and falling to the ground) and screaming—established patterns of collective celebrity worship that directly prefigured later movements such as Elvis Presley fandom and Beatlemania.

The defining element of the attire was the namesake bobby socks, short white ankle-length socks that were carefully folded down at the cuff. These were invariably paired with sturdy low-heeled saddle shoes (black-and-white oxfords) or penny loafers.

Upper garments favored a casual, schoolgirl aesthetic, often consisting of Shetland wool sweaters or sweater sets worn over simple white blouses. These were usually combined with pleated skirts or, later in the 1950s, the full poodle skirt, though cuffed denim jeans were sometimes worn in less formal settings. Accessories were minimal but included identification bracelets and bows or ribbons securing their long hair.

Grooming emphasized a natural, youthful look, avoiding heavy makeup in favor of a subtle painted nail polish. The subculture's emphasis on uniformity and conformity was absolute, distinguishing them from adults' fashion. Social rituals revolved around public leisure that utilized this style. This included attending sock hops (informal dances where shoes were removed to protect the floor), loitering at soda fountains, and gathering at the movies or concerts to engage in collective emotional displays of fandom.

The behaviors and aesthetic of the Bobby-Soxers elicited widespread concern among parents, cultural critics, and authorities in the mid-1940s, creating a notable moral panic. Parents worried that the girls' intense emotional devotion to Frank Sinatra would lead to delinquency, impact their burgeoning sexuality, and alienate them from family values. The public swooning, screaming, and fainting at concerts were frequently interpreted by media outlets as signs of "mass hysteria" or "mass sexual delirium," reflecting deep-seated societal anxieties about youth autonomy and the loss of emotional control among adolescent girls. This led to exaggerated, often satirical, portrayals in films and newspapers that reinforced stereotypes of the girls as juvenile, emotional, and public safety threats.