American progressive metal side project started by drummer Mike Portnoy of Dream Theater. Active between 1997-1999, regrouped in 2007 (as a trio Liquid Trio Experiment) and again in 2008 (full band). By their second release, Liquid Tension Experiment 2 (1999), Jordan Rudess had also joined Dream Theater as their keyboardist, making Liquid Tension Experiment 3/4 Dream Theater members. For this reason they decided not to continue the project, although they played some shows in 2008 in order to celebrate their 10th anniversary.

Band officially returned in 2020 and released their third album in Spring 2021.