ICQ is an open source instant messaging computer program that was first developed and popularized by the Israeli company Mirabilis in 1996. The name ICQ stands for "I Seek You". Its ownership was passed to AOL in 1998 and to Mail.Ru Group in 2010.

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 the first stand-alone instant messenger and the first online instant messenger service as such — 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.