Formal wear or full dress is the 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. Generally permitted other alternatives, though, are 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 (which preceded morning coat as default formal day wear 1820s-1920s). In addition, formal wear is often instructed to be worn with official full size orders and medals.

The protocol indicating particularly men's traditional formal wear has remained virtually unchanged since the early 20th century. Despite decline following the counterculture of the 1960s, it remains observed in formal settings influenced by Western culture: notably around Europe, the Americas, South Africa, Australia, as well as Japan. For women, although fundamental customs for formal ball gowns (and wedding gowns) likewise apply, changes in fashion have been more dynamic. Traditional formal headgear for men is the top hat, and for women picture hats etc. of a range of interpretations. Shoes for men are dress shoes, dress boots or pumps and for women heeled dress pumps. In western countries, a "formal" or white tie dress code typically means tailcoats for men and evening dresses for women. The most formal dress for women is a full-length ball or evening gown with evening gloves. Some white tie functions also request that the women wear long gloves past the elbow.

Formal wear being the most formal dress code, it is followed by semi-formal wear, equivalently based around daytime black lounge suit, and evening black tie (dinner suit/tuxedo), and evening gown for women. The male lounge suit and female cocktail dress in turn only comes after this level, traditionally associated with informal attire. Notably, if a level of flexibility is indicated (for example "uniform, morning coat or lounge suit", such as seen to the royal wedding of Prince Harry and Meghan Markle in 2018), the hosts tend to wear the most formal interpretation of that dress code in order to save guests the inconvenience of out-dressing.

Since the most formal versions of national costumes are typically permitted as supplementary alternatives to the uniformity of Western formal dress codes, conversely, since most cultures have at least intuitively applied some equivalent level of formality, the versatile framework of Western formal dress codes open to amalgamation of international and local customs have influenced its competitiveness as international standard. From these social conventions derive in turn also the variants worn on related occasions of varying solemnity, such as formal political, diplomatic, and academic events, in addition to certain parties including award ceremonies, balls, fraternal orders, high school proms, etc.