DRESSCODES: Evening dress codes were simple in Victorian and Edwardian times. 

Any occasion where women were present was implicitly considered formal and called for men to be attired in a tailcoat and appropriate full-dress accompaniments.  Stag affairs, on the other hand, were regarded as informal and permitted the use of a dinner jacket if gentlemen preferred.
One of the primary drawbacks of discarding rules for appropriate dress is that "unbridled freedom often leads to chaos, confusion, frustrations and terrible insecurity."   Debrett's New Guide to Etiquette and Modern Manners - Britain's authoritative etiquette guide  echoes these sentiments in the quotation at the top of this page.  However, the book's author also points out that the tide is turning:  
This is because of two fundamental human instincts that have been overlooked by the slobs.  One is the ancient need of people to decorate themselves, which started long before the first murmuring of civilisation and continues today.  The other is our very natural wish to please others, be admired by our peers and attract a mate.  Add to this the security that a few unwritten rules can bring, and the enduring need for dressing up becomes clear.
Contemporary American etiquette sources, on the other hand, prefer the post-war or modern interpretations of the various codes but divide the most formal category into sub-categories to allow the inclusion of both the tailcoat and the tuxedo (and sometimes even the dark suit). These sub-categories are often explicitly designated as White Tie or Black Tie. As with the traditional guidelines, male guests usually dress one category below the groomsmen.
Afternoon weddings with evening receptions pose a particular problem in that evening wear should not be worn before six o'clock.  If you are planning such a wedding and don't wish the ask the wedding party (and guests) to change before dinner then the traditional rule is that morning dress (formal daytime dress) is allowable in the evening on such occasions.  Alternately, you may wish to take advantage of the etiquette exceptions that allow for evening wear to be worn prior to six.  One exclusion is that “evening” can be defined as 6 o’clock or dark, whichever comes first.  Another is that it is allowable to wear evening dress prior to six provided that a person is on his way to an evening function.
For summer or tropical weddings that require tuxedos a white dinner jacket is a popular  and correct  alternative.  At all other times only the traditional form of black tie should be worn to a wedding; both conventional and modern authorities agree that this is not an appropriate time to be creative.

The elements of black tie:

Unlike white tie, a man has sartorial options in choosing his dinner jacket and accessories. The elements of a traditional black-tie ensemble are:

    * Short or medium black jacket which may have grosgrain- or satin-faced lapels
    * Black trousers with or without silk braids matching the lapels
    * A black cummerbund or a low-cut waistcoat
    * A white dress shirt with either a marcella or a pleated front
    * A black silk bow tie
    * Black dress socks, often made of silk
    * Black patent leather shoes or highly polished black leather shoes

Jacket

The typical black-tie jacket is single-breasted, ventless, constructed of black or midnight blue wool, which may be faced with either grosgrain (ribbed silk) or satin. The most traditional lapel type is the peaked lapel, derived from its tailcoat predecessor; the shawl collar (with rounded lapels) is used also. Currently, both styles can be either single- or double-breasted. A third lapel style, the notched lapel, is an American innovation, and is considered "fashion-forward" rather than traditional. The traditional single-breasted jacket has a single-button closure, with two-button variants sometimes seen; jackets incorporating more buttons are fashion fads. (Also see: smoking jacket)

The colour black may have a green hue in artificial light, if aesthetically unacceptable to the man, midnight blue (introduced by the Prince of Wales) is the acceptable alternative colour; other colours are fads.

The white dinner jacket is often worn in warm climates. The American colour exceptions are its use in the celebratory high school graduation promenade dance, or "prom", and concert conductors, i.e. the Last Night. In the U.S. and Canada a white dinner jacket is traditionally worn only from Memorial Day in the spring to Labor Day in late summer, this rule applies also to white summer clothes (shoes, suits, et cetera).

Stylistically, it is bad form (ill-mannered) for a man to take off his jacket during a black-tie social event; but when hot weather and humidity dictate, the ranking man (of the royal family, the guest of honour) may give men permission by noticeably taking off his jacket. In anticipated hot weather Red Sea rig is specified in the invitation, although this dress is esoteric in civilian circles, and is particular to certain communities.

Trousers

Black-tie suit trousers have no turn-ups (cuffs) or belt loops. The outer leg seams may be decorated with a single, silk braid matching the lapel facing. Customarily, braces (suspenders in the U.S.) hold up the trousers; they are hidden either by the waistcoat, which may be backless, or by the coat: hence it is bad social form for a man to take off his coat. Recently, flat-front, pleatless trousers feature in some styles of dinner dress; like all innovations in formal wear the feature's appropriateness is debated.

Waistcoat or Cummerbund

The waist is dressed in either a waistcoat (vest) or a cummerbund (not both) when wearing a single-breasted coat. Usually, the waistcoat is low-cut, has a three-button stance, and of the same cloth as the jacket. The cummerbund sash (from military dress uniform in British India) is worn pleats up, and is of the same cloth as the bow tie and lapels. (White waistcoats with black tie are a rare alternative.)
A cummerbund is a broad waist sash, usually pleated, which is often worn with single-breasted dinner jackets [1]. The cummerbund was first adopted by British military officers in colonial India and later spread to civilian use. The modern day use of the cummerbund is as a component of semi-formal or black tie dress.
The name comes from the Persian for waist restraint (kamar "waist" and band from Sanskrit which means "to close") and was borrowed into English from the Hindi word meaning "loinband" in 1616. The word "cummerband" (see below), and less commonly the German spelling "kummerbund", are often used synonymously with "cummerbund" in English. The word is also quite commonly misspelled and mispronounced as "cumberbun".
Cummerbunds were traditionally worn with pleats facing up in order to hold ticket stubs and similar items. The contemporary use of the cummerbund is purely aesthetic.

Shirt

The Shirt is conventionally white or off-white (cotton, linen, silk) and its front either is cotton marcella (as in white tie) or pleated.

Before World War II, stiff shirts with separate wing collars were the norm. Today, semi-stiff shirts with attached wing collars are the U.S. norm; a shirt with a fold-down collar is the U.K. norm. The original, and most formal, version of the dress shirt usually fastens with matching shirt studs and cuff links. In lieu of studs, a buttoned shirt with either a fly-front placket or a French front (sans placket) is worn. Soft shirts have French cuffs, stiff shirts (as in white tie) have single cuffs fastened with cuff links.

Bow Tie

The Bow Tie is typically made of silk barathea or satin and is knotted by hand. It is considered poor form and déclassé by some to wear a commercially pre-knotted clip-on or hook fastened bow tie, or especially when the clips or (hook-and-buckle) fastener shows. Yet, for most black tie occasions, such a pre-knotted bow tie is common, given that most black tie clothes are hired, not owned; the stigma of appearing the boy-dressed-as-a-man is lessened. Moreover, in the 1980s and 1990s, the manually tied and knotted bow tie has almost vanished beyond the upper social stratum. Many ascribe no stigma of inelegance to the commercial, pre-knotted bow tie, and would require instruction to tying and knotting a properly formal bow tie.

Footwear

Traditionally, the most formal shoes are patent-leather opera pumps (court shoes) decorated with a ribbed silk bow, as worn with white tie; they are uncommon today. A popular, formal alternative is the black leather lace-up Oxford shoe, often in patent leather, but without a toe cap or decorative brogueing. Too-informal for black tie are shoes with open lacing, i.e. "Derbies" in the U.K., "bluchers" in the U.S. An exceedingly rare alternative is the black button boot.

Hosiery should be black, knee-high, ribbed silk socks.

Accessories

Handkerchief and Boutonniere: A white handkerchief (cotton, linen or silk) and/or a boutonniere (a blue cornflower, red or white carnation, or a rosebud.) may be worn on the coat.

Outerwear: In cold weather a chesterfield overcoat, gray gloves, and a white silk scarf are worn.

Hat: Black tie has no standard hat. If one is worn, it usually is a black homburg or trilby in winter; in summer, a straw boater is acceptable. Top hats are worn only with white tie and morning dress.

Timepiece: If worn, a wristwatch should be slender, plain, and elegant; alternatively, a pocket watch may be worn on the waistcoat. Traditionally, however, visible timepieces are not worn with formal evening dress, because timekeeping is not considered a priority.

Decorations and orders: Military, civil, and organisational decorations usually worn only to formal events of State or other sovereign organisation. Miniature orders and awards are typically worn on the left breast or left lapel of the jacket, and neck badges, breast stars, and sashes are worn according to country-specific or organisational regulations.

Black-Tie Social Occasions

Black tie is worn to private and public dinners, dances, and parties. At the formal end of the social spectrum, it replaced white tie where it once was de rigueur dress (e.g. for orchestra conductors).

Black tie is evening dress, worn only after six o'clock in the evening, or after sundown during winter months. Black tie's daytime equivalents are morning dress for formal daytime events, or the stroller for semi-formal day events.

Black Tie in public perception

    * Given the nature of black tie social dress, the dinner jacket is considered exclusive; ownership is a statement of caste.
    * Some deride the dinner jacket as "penguin suit", connoting conformism.