Formal dress code is a Western dress code category applicable for the most formal occasions, such as weddings, christenings, confirmations, funerals, Easter and Christmas traditions, in addition to certain state dinners, audiences, balls, and horse racing events. Formal wear is traditionally divided into formal day and evening wear, implying morning dress (morning coat) before 6 p.m., and white tie (dress coat) after 6 p.m. Formal wear is the most formal dress code, followed by semi-formal wear, which is equivalently based around daytime black lounge suit, and evening black tie (dinner suit/tuxedo), and evening gown for women.

For men, formal attire indicates a black tie event, which means a black tuxedo and a tuxedo shirt. For women, a formal dress code usually means a formal, floor-length evening gown with jewelry, heels, and an elegant clutch. Formal wedding attire sits between cocktail and black tie on the wedding dress code scale. Women can get away with a nicer cocktail dress, and for men, tuxedos are not required. Formal wedding attire (synonymous with black-tie optional attire) offers more flexibility than black tie, so dressy separates and dresses that hit above the ankle are acceptable, as well as fitted, darker-hued suits paired with a crisp white button-down and tie.

In addition to tuxedos and evening gowns, other alternatives that are permitted for formal wear include the most formal versions of ceremonial dresses (including court dresses, diplomatic uniforms, and academic dresses), full dress uniforms, religious clothing, national costumes, and most rarely frock coats. When a level of flexibility is indicated, the hosts tend to wear the most formal interpretation of that dress code in order to save guests the inconvenience of out-dressing.