Black tie is a dress code for formal evening events, and is worn to many types of social functions. For a man, the major component is a jacket, known as a dinner jacket (in the Commonwealth of Nations) or tuxedo (mainly in the United States), which is usually black but is sometimes seen in other colours. Analogues for women's evening dress range from a conservative cocktail dress to the long evening gown, determined by current fashion, local custom, and the occasion's time.

The term tuxedo is itself variously used in different parts of the world. It always refers to some form of dinner jacket, and sees most use in North America, where the term originated. There, it is commonly taken to mean a modern variation on the traditional black tie, while in Britain, it is sometimes used to refer to the white jacket alternative.

Black tie dates from 1860, when Henry Poole & Co. (Savile Row's founders - just off Bond Street, historically London's high-end fashion shopping centre) created a short smoking jacket for the Prince of Wales (later Edward VII of the United Kingdom) to wear to informal dinner parties as an alternative to white tie dress—the standard formal-wear. At that time, lounge suits were starting to be worn in the country, and the new dress code was an evening lounge suit intended for use in a relaxed atmosphere out of town.

In the spring of 1886, the Prince invited James Potter, a rich New Yorker, and his wife, Cora Potter, to Sandringham House, his Norfolk hunting estate. When Potter asked the Prince's dinner dress recommendation, he sent Potter to Henry Poole & Co., in London. On returning to New York in 1886, Potter's dinner suit proved popular at the Tuxedo Park Club; the club men copied him, soon making it their informal dining uniform. The evening dress for men now popularly known as a tuxedo takes its name from Tuxedo Park, where it was said to have been worn for the first time in the United States, by Griswald Lorillard at the annual Autumn Ball of the Tuxedo Club founded by Pierre Lorillard IV, and thereafter became popular for formal dress in America. Legend dictates that it became known as the tuxedo when a fellow asked another at the Autumn Ball, "Why does that man's jacket not have coattails on it?" The other answered, "He is from Tuxedo Park." The first gentleman misinterpreted and told all of his friends that he saw a man wearing a jacket without coattails called a tuxedo, not from Tuxedo.

Two years later, it gained the name dinner jacket (DJ) in Britain, a name it has also kept in the North-Eastern U.S.

While in America the new garment was initially called a tuxedo, the term has since been inaccurately used, particularly in America, to denote any form of formal or semi-formal dress including white tie, morning dress, and strollers.

Unlike white tie, which is very strictly regulated, black-tie ensembles can display more variation. In brief, the traditional components are:

The typical black-tie jacket is single-breasted, ventless, and black or midnight-blue; usually of wool or a wool–mohair blend. Double breasted models are less common, but are equally acceptable. The lapels may be faced with silk in either a grosgrain or less traditional satin weave. Traditionally there are two lapel options, the shawl collar, derived from the smoking jacket, and the peak lapel, from the tailcoat. The former is older, while the latter is considered more formal. A third lapel style, the notched lapel, has only recently gained popularity, and has been accepted by some as "a legitimate ... less formal alternative," although, despite some precedent, it is disdained by purists for its lounge suit derivation. In France, Italy, Brazil, Germany and Spain, the jacket is called smoking. In France the shawl-collared version is le smoking Deauville, while the peaked-lapel version is le smoking Capri.

The double-breasted jacket is slightly more modern than the single-breasted, and less formal; while it was originally considered acceptable only for wear at home (similarly to Prince Albert slippers or a smoking jacket), it is now equally correct in all situations, though traditional rules regarding slightly different selections of accessories may be followed. While more common with a peaked lapel, a shawl lapel is appropriate. All buttons that can be done up, are, including any inner ones which might normally be left undone on a double-breasted lounge suit. While two-button variants are sometimes seen, the traditional single-breasted jacket has a one-button closure.

Black was known to take on a green hue in early artificial lights, hence midnight blue was introduced by the Prince of Wales (later Duke of Windsor), and remains the only acceptable alternative colour for the standard dinner jacket.