Internet homicide, also called internet assassination, refers to killing in which victim and perpetrator met online, in some cases having known each other previously only through the Internet. Internet killer is also an appellation found in media reports for a person who broadcasts the crime of murder online or who murders a victim met through the Internet. Depending on the venue used, other terms used in the media are Internet chat room killer, Craigslist killer, Facebook serial killer. Internet homicide can also be part of an Internet suicide pact or consensual homicide. Some commentators believe that reports on these homicides have overemphasized their connection to the Internet.

Serial killers are murderers who target three or more victims sequentially, with a "cooling off" period between each murder, and whose motivation for killing is largely based on psychological gratification. Such killers have used forms of social networking to attract victims long before the advent of the Internet. For example, between 1900 and 1914, Hungarian serial killer Béla Kiss lured his 24 victims by using personal ads published in newspapers.

According to Paul Bocj, the author of Cyberstalking: Harassment in the Internet Age and How to Protect Your Family, "The idea that a serial killer may have operated via the Internet is, understandably, one that has resulted in a great deal of public anxiety." In Harold Schecter's A to Z Encyclopedia of Serial Killers, the entry for "Internet" reads in part: "If the Internet has become a very useful tool for people interested in serial killers, there's some indication that it may also prove to be a resource for serial killers themselves." Maurice Godwin, a forensic consultant, argued that "There are some sadistic predators that rely on the Mardi Gras Effect ["the ability to hide one's identity on the Internet"] to lure and murder repeatedly." The first serial killer known to have used the Internet to find victims was John Edward Robinson, who was arrested in 2000 and was referred to in Law Enforcement News as the "USA's first Internet serial killer" and "the nation's first documented serial killer to use the Internet as a means of luring victims."

Online predators, participants in internet suicide and suicide-homicide pacts, and internet killers may seek out victims through internet forums, chat rooms, listservs, email, bulletin boards, social networking sites, online role playing games, online dating services, Yahoo groups, or Usenet.

Online chatrooms are sometimes used by killers to meet and bait potential victims. For example, the Japanese serial murderer Hiroshi Maeue is known to have found victims by using online suicide chat rooms. The killer Lisa Marie Montgomery is reported to have met her victim in an online chatroom for rat terrier lovers called "Ratter Chatter."

Online chatrooms are also used, in some cases, to plan consensual homicides. For example, in 1996, a Maryland woman, Sharon Lopatka, apparently agreed to be killed by torture and strangulation in a conversation with a man in an online chatroom. Robert Frederick Glass pleaded guilty to killing Lopatka and later died in prison while serving his sentence. In a case that might be regarded as a quasi-consensual homicide, "John," a teenage boy from Altrincham, England, allegedly tricked another teenager into killing him using long conversations in an online chatroom. The other teenager, Mark, apparently believed he was being recruited by a female Secret Service agent. The suicide-by-homicide failed and on May 29, 2004 John pleaded guilty to inciting someone to murder him and was sentenced to three years supervision. Mark pleaded guilty to attempted murder and was sentenced to two years supervision. The boys were forbidden to contact each other.

As an article in the New York Daily News explained in 2009, "Long before there was a craigslist or dot-com dating, there were places where men and women who were too shy or busy to meet face to face could find romance. Calling themselves "matrimonial bureaus," these organizations were known mostly as the "lonely hearts clubs," and they flourished through the middle of the 20th century." It was in venues like these—print media such as newspaper classified ads and personal or lonely hearts club ads—that 20th century murderers such as Harry Powers, the so-called "Matrimonial Bureau Murderer," and Harvey Carignan, "the Want Ad Killer" met their victims.

Electronic advertising has gradually replaced printed ads and the Internet is now a venue where murderers who employ a similar modus operandi can meet their victims; in Schecter's Encyclopedia, the entry for "Ads" mentions Internet dating and the use of Internet ads by the so-called "Internet Cannibal" Armin Meiwes. Since 2007, several accused and convicted killers have contacted victims through advertising services such as Craigslist, a popular classified advertising website. These killers are sometimes referred to in the media as "Craigslist killers"; the first use of the term Craigslist killings may date to October 31, 2007, when the phrase appeared in a headline in the Saint Paul Pioneer Press in Minnesota, in reference to the murder of Katherine Olson by Michael John Anderson, who was then dubbed "the Craigslist killer".