The first version of the program was released in November 1996 and ICQ became the first Internet-wide instant messaging service, later patenting the technology. AOL acquired Mirabilis on June 8, 1998, for US$407 million.

In April 2010, AOL sold ICQ to Digital Sky Technologies for $187.5 million. According to Time Warner, ICQ has over 100 million accounts registered.

Mirabilis was first established by five Israelis: Yair Goldfinger, Sefi Vigiser, Amnon Amir, Arik Vardi, and Arik's father Yossi Vardi. They recognized that many people were online accessing the Internet through a non-UNIX operating system, and that there was no software that enabled an immediate connection between them.

What was missing was the technology for locating and connecting the users of the Windows operating system.

The technology Mirabilis developed for ICQ was distributed free of charge. The technology's success caused AOL to acquire Mirabilis on June 8, 1998, for US$407 million. At the time, this was the highest price ever paid to purchase an Israeli technology company.

QQ, a Chinese instant messaging program and network, originally used the name OICQ. This name conflicted with ICQ, and the company changed the name to QQ.

ICQ's Management changed at the end of 2003. Under the leadership of the new CEO, Orey Gilliam who also assumed the responsibility for all of AOL's Messaging business in 2007, ICQ resumed its growth and turned into a highly profitable company, and one of AOL's most successful businesses.

Eliav Moshe replaced Gilliam in 2009 and became ICQ's Managing Director.

ICQ provides all users additional services and content products:

ICQ users are identified by numbers called UIN, distributed in sequential order. The UIN was first invented by Mirabilis, as the user name assigned to each user upon registration. The meaning is either Universal Internet Number or Unified Identification Number. Issued UINs started at number 10000 (5 digits) and every user receives a UIN when first registering to ICQ. As of ICQ6, users are also able to log in using the specific e-mail address they associated with their UIN during the registration process. Unlike other instant messaging software or web applications, on ICQ the only permanent user info is the UIN, although it is possible to search for other users using their associated e-mail address or any other detail they have made public (by updating it in the public profile). In addition, the user can change all of his or her personal information, including screen name and e-mail address, without having to re-register. Since 2000, ICQ and AIM users are able to add each other to their contact list without the need for any external clients. As a response to UIN theft or sale of attractive UINs, ICQ started to store email addresses previously associated to a UIN. As such, UINs that are stolen can sometimes be reclaimed. This applies only if (since 1999 and onwards) a valid primary email address was entered into the user profile.