Many specialist online dating services or other Internet websites, known as "adult personals" or "adult matching" sites, cater to people looking for a purely physical relationship, without emotional attachments.
During the sexual revolution in the United States and Europe in the 1960s and 1970s, social attitudes to sexual issues underwent considerable changes.
A study of hooking up at the University of Iowa found that waiting to have sex doesn't contribute to a stronger future relationship.
Instead, they found that what mattered most was the goal individuals had going into a relationship.
Hooking up became a widespread practice among young people in the 1980s and 1990s.
Researchers say that what differentiates hooking up from casual sex in previous generations of young people is the "virtual disappearance" of dating, which had been dominant from the postwar period onwards.