OkCupid (sometimes abbreviated as OKC ) is an American-based international operating online dating, friendship, and social networking website that features member-created quizzes and multiple-choice questions. It is supported by advertisements and paying users who do not see ads.
The site supports multiple modes of communication, including instant messages and emails. OkCupid was listed in Time magazine's 2007 Top 10 dating websites.  The website was acquired by IAC's Match.com division in 2011. 
OkCupid was initially owned by Humor Rainbow, Inc. OkCupid's founders (Chris Coyne, Christian Rudder, Sam Yagan, and Max Krohn) were students at Harvard University when they gained recognition for their creation of TheSpark and, later, SparkNotes. Among other things, TheSpark.com featured a number of humorous self-quizzes and personality tests, including the four-variable Myers-Briggs style Match Test. SparkMatch debuted as a beta experiment of allowing registered users who had taken the Match Test to search for and contact each other based on their Match Test types. The popularity of SparkMatch took off and it was launched as its own site, later renamed OkCupid. The current OkCupid Dating Persona Test is still largely identical, in question and text blurb content and order, to the original Match Test. In 2001, they sold SparkNotes to Barnes & Noble, and began work on OkCupid. 
In 2008, OkCupid spun off its test-design portion under the name Hello Quizzy (HQ), while keeping it inextricably linked to OkCupid and reserving existent OkCupid users' names on HQ.
Since August 2009, an "A-list" account option is available to users of OkCupid and provides additional services for a monthly fee. 
In February 2011, OkCupid was acquired by IAC/InterActiveCorp, operators of Match.com, for US$50 million.  Editorial posts from 2010 by an OkCupid founder in which Match.com and pay-dating were criticized for exploiting users and being "fundamentally broken" were removed from the OkCupid blog at the time of the acquisition.  In a press response, OkCupid's CEO explained that the removal was voluntary. 
The website added a bevy of nontraditional profile options for users to express their gender identity and sexuality in late 2014. These options—which included asexual, genderfluid, pansexual, sapiosexual, and transgender categories—were added to make the website more inclusive. 
Rudder updated the "OkTrends" blog, which consists of "original research and insights from OkCupid," for the first time in three years in July 2014. Entitled "We Experiment On Human Beings!," the post discusses three experiments run by the website without the knowledge of users. Rudder prefaces the experiment results by stating: "... if you use the Internet, you're the subject of hundreds of experiments at any given time, on every site. That's how websites work." 
In May 2016, a team of Danish researchers have made publicly available the "OkCupid dataset" project, containing (as of May 2016) 2,620 variables describing 68,371 users on OkCupid for research purposes (e.g., for psychologists investigating the social psychology of dating).  The data release spurred considerable criticism,  included an investigation by the Danish Data Protection Authority. 
OkCupid claimed 3.5 million active users as of September 2010. According to Compete.com, the website attracted 1.3 million unique visitors in February 2011. 
The site used to have a highly active journal/ blogging community as well. Journals are not available to new members and the feature is now "retired." Members have the option of saving favorite user profiles, which display the favorited person's responses to questions and profile updates on the member's front page.
Any adult may join the site and all users may communicate with others via private messages or an instant messaging "chat" function. OkCupid was the first major dating site to offer unlimited messaging free of charge.  A-List (paying) members see no advertising and have more filtering options and preferential placement in an "A-List Matches" section of search results. A-list members can also browse openly while choosing whether or not their profile is displayed to those they visited. 
OkTrends, the official blog of OkCupid, presents statistical observations from OkCupid user interactions, to explore data from the online dating world.
To generate matches, OkCupid applies data generated by users' activities on the site,  as well as their answers to questions. When answering a question, a user indicates his or her own answer, the answers he or she would accept from partners, and the level of importance he or she places on the question. The results of these questions can be made public. OkCupid describes in detail the algorithm used to calculate match percentages. Assuming a user is a paid user ("A-List"), the site notifies a user if someone likes that user.
Attractiveness and match results
Users who receive high ratings may be notified by email that they are in the "top half of OkCupid's most attractive users" and "will now see more attractive people in [their] match results". The email also reads "And, no, we didn't just send this email to everyone on OkCupid. Go ask an ugly friend and see".