Many times an official party or organized celebration can be too regulated or formal for guests to feel completely relaxed. Other times, an event may end so late in the evening that a traditional reception or party would be impractical. This is why many people choose to attend a much less formal event known as an after party. An after party is literally the party which follows the party.

While a high school prom may be held on school property and require a formal or semi-formal dress code, for example, an after party is often held in a private home or rented venue. An after party following an awards banquet or movie premiere may be hosted in a restaurant or privately sponsored. The point of an after party is to provide an informal atmosphere following a formal event.

Unlike a formal reception or organized party, an after party is generally expected to be a casual affair from start to finish. The hosts may hire a DJ or live band to provide dance music for guests, and there is rarely any form of dress code. Food served at a typical after party may be closer to heavy appetizers or pub grub than a formal meal. An open bar complete with a dedicated bartender is often provided at an after party for adult party goers. An after party is often called a house party, since many organizers use their own homes instead of renting a more formal venue.

An after party often gives professional musicians and performers an opportunity to unwind after performances or official industry parties. It can also allow prom goers a chance to spend time with their intimate circle of friends after such a large public event. The after party can also provide an opportunity for the formal event organizers to relax after finishing their official hosting duties. Many times guests find it easier to socialize at an after party, since a formal reception or awards banquet may not allow guests to mingle as freely as they would like. A casual after party atmosphere encourages guests to introduce themselves under far less formal circumstances.

The after parties held after such events as the Academy or Tony Awards have become almost as well-known as the organizations themselves. Following the broadcast of the awards ceremony, many notable celebrities make the rounds of official and unofficial after parties. An after party may not even begin until very late in the evening, and many have been known to last until the early morning hours. A late night after party for actors or musicians may take place in an after-hours bar or private club, since traditional bars may have to stop serving alcoholic beverages by a designated hour. Whatever the venue, a good after party allows guests to wind down gradually after attending a formal party or organized social event.