The ICQ client application and service were initially released in November 1996 and the client was freely available to download. Users could register an account and would be assigned a number, like a phone number, for others to be able to contact them (users could also provide handles). ICQ was among the first stand-alone instant messenger and the first online instant messenger service — while real-time chat was not in itself new to the internet (IRC being the most common platform at the time), the concept of a fully centralized service with individual user accounts focused on one-on-one conversations set the blueprint for later instant messaging services like AIM, and its influence is seen in modern social media applications. Whilst Internet Relay Chat programs, like Pirch and mIRC, dominated the market for many years, their popularity began to fall in the face of mobile computing which had begun to take hold with PalmPilot and the fledgling Microsoft Windows Compact Edition.
At its peak around 2001, ICQ had more than 100 million accounts registered. At the time of the Mail.Ru acquisition in 2010, there were around 42 million daily users. Since 2013, ICQ has 11 million monthly users.
ICQ6 was launched on April 17, 2007, and offered a single communication platform that combines the various user options: instant messaging services, free SMS from ICQ to mobile, voice and video communication. The software's sounds were created by the Israeli psychedelic trance duo Infected Mushroom. Among the new additional features in ICQ6 are Quick IM, which allows users to send a short message without opening a conversation window, a "follow me" service directly to the user’s mobile, a multi-chat service and support for Zlango, the animatedicons language.
ICQ provides all users additional services and content products:
ICQ TV—An online video magazine. The magazine broadcasts content for teens 24/7.
ICQ Game Center—A games platform that enables the user to play with and/or against other users. Available by clicking a button in the contact list.
ICQ2Go—A web instant messaging option for users who cannot download the program onto their computers or use it on the networks they are accessing (for various reasons, like security restrictions or firewalls).
ICQ for Mac (Beta)—Released in February 2010, a version of the client that was developed using the Adobe AIR platform, making it usable on additional operating systems which support the AIR runtime, such as Linux.
Also, users can choose and select their own avatars for their profile pages. In this way, they can protect their privacy.