In the context of BDSM, bondage involves people being tied up or otherwise restrained for pleasure. Bondage is usually, but not always, a sexual practice. The paraphilia of being sexually aroused by bondage is sometimes known as vincilagnia.
Studies in the U.S. have shown that about a half of all men find the idea of bondage to be erotic; many women do as well. As with any study of sexual thoughts and behavior, the available studies are not well controlled and the best studies are now out of date.
It is worth noting that bondage has sexual appeal to persons of both sexes and all sexual orientations. However, a subculture of homosexual men, sometimes called leathermen, were arguably among the first group to make obvious hints of their tastes in bondage in public.
The leathermen emulated the biker culture that arose after World War II. While the bikers were not identified as homosexual, the leathermen admired their toughness, tenacity, and willingness to ignore mainstream social mores. Consequently, they adopted the biker style of dress, particularly the use of black leather. While this served a utilitarian purpose for the bikers, in providing warmth and protection from "road rash", it was primarily of fashion and fetishistic value to the leathermen, who for the most part did not ride motorcycles extensively.
Beginning in the late 1960s, heterosexual groups began to come together to explore bondage and power exchange. With time these groups have grown and have raised their profile somewhat, to the point where most U.S. cities of any size have one or more such groups. A major goal of most of these groups is to provide semi-public opportunities for BDSM, in an effort to provide a safe environment for relative strangers to engage in such activities. As such, these groups attach high importance to objective safety rules, such as the use of safewords.
Although reliable data is unavailable, the financial success of companies that market bondage equipment testifies to the fact that it is more than fantasy to many and that a sizeable proportion of couples have made regular use of bondage in their sexual activities at some point in their relationships.
For the most part, such bondage/b> games end in sex. In contrast, bondage games between more casually acquainted players in the BDSM subculture frequently end in masturbation only, or in some cases include no sexual release at all.
Safety rules followed by couples in a committed relationship are frequently more subjective and trust-based. These differences can lead to culture clash where a couple with a history of bondage games together encounters the BDSM subculture: the couple can't understand the insistence upon safewords, while the members of the subculture can't understand the focus on sexual intercourse.

Two women tapegagged and cuffed to iron bars
Studies of men's sexual fantasies have shown that the fantasy of being bound during intercourse is second in frequency only to the basic fantasy of sex with a voluptuous nude woman. Consequently, it should be no surprise that bondage themes have been present in pornography for some time.
Bondage pornography for heterosexual men almost overwhelmingly depicts bound women, rather than bound men, in spite of the most common fantasy in both sexes being one of being bound, rather than of being the dominant. This may be because many men fear becoming aroused by pictures of other men, and are more willing to identify with a bound woman. It may also be because pictures of bound women allow them to vicariously experience both the heterosexual male dominant and female submissive fantasies.
However, there is the persistent yet small niche of crossdressed men in bondage that has been depicted in photographs and videos published by Harmony Concepts since the early 1970's. Since the advent of the internet, the world wide web has provided a steady medium for fetish models, such as Delilah Knotty to express the transgendered roll of men in bondage. Today the internet provides views of human bondage in nearly all aspects not traditionally shown in mainstay pornography.
Early examples of bondage erotica include:
Bondage can be divided into six main categories:

Rope is a commonly used bondage device
Some of the large variety of restraints used in bondage:
Some simple bondage techniques:
Some more complex techniques:
There are also some common fantasy settings in which bondage is often played:
Bondage is often combined with other sexual and BDSM techniques. See list of bondage positions and list of bondage equipment for more details.
Technique in self-bondage is more complex, involving special methods to apply the bondage to oneself, and also to effect a release after a lapsed period of time. Self-bondage is also notably risky: see the safety notes below.
Many people regard bondage as safe when conducted between relatively sober, trusted partners who are fully aware of the risks involved and the precautions necessary to ensure safety. Partners who are in committed relationships may have a greater basis for trusting each other. Performing acts in a supervised location, such as a dungeon, or with a group of trusted friends may also increase safety.
There is also a subculture of people who seek out others interested in bondage and pursue such activities with people who they do not know well. This subculture has given rise to the safe, sane and consensual credo.
Safety precautions include:
One very simple safety measure is to, every so often, ask the subject if he or she is all right. Another is to check body parts like hands and feet for numbness or coldness, which can happen if nerves have been pinched or blood circulation has been blocked. Another is to check for skin discolouration. Skin that does not get enough oxygen turns bluish. If blood can get in, but can't get out because one of the veins has been blocked, that part of the body turns purple.
If the subject has been gagged or can otherwise not verbally communicate, a different form of the safeword is needed. For instance, they may hum a simple tune, or an object in one hand (typically a ball) can be released.
Some simple preparations may also be helpful:
It should be noted that scenes depicted in bondage photographs and videos are chosen for their visual appeal and fantasy value. In most cases they cannot be "acted out" with good results.
Self-bondage carries a higher risk, particularly because it violates the first principle of bondage safety: to never leave a bound person alone. Without someone to release them in the event of an emergency or medical crisis, self-bondage can be lethal to its practitioners. It has been estimated in the medical literature there are around 500-1000 deaths every year in the United States due to autoerotic asphyxia (self-strangulation) alone.
People who find it erotic to be tied up find it so for a variety of reasons:
People who enjoy tying other people up are motivated by a variety of reasons, including:
The mechanics of bondage are trivial compared to the relationship issues.
Some members of the BDSM subculture take another route and seek out partners who share their interest in bondage. Many act out their bondage fantasies within the confines of private "play" parties where overt genital contact is not allowed between participants.
Some bondage practitioners go through a process often called "negotiation" with potential partners, be they long time partners or more casual relationships. Negotiation is essentially a conversation conducted well before any sexual activity has begun in which each party frankly outlines what they are interested in and what their boundaries are, and out of that shared information comes to a mutual agreement about potential bondage play in upcoming sexual activity. Although some people may find this embarrassing at first, this frank and forthright exchange allows both parties to feel confident about bondage activity and to understand their partner's needs. Due to the vast range of activities and intensities that are possible in bondage play and fetish sex, negotiation is an excellent technique to make sure both parties have realistic expectations and that the anticipated acts will be enjoyable to all involved.