Lubuntu is a lightweight Linux distribution based on Ubuntu, using the LXQt desktop environment in place of Ubuntu's GNOME desktop. Lubuntu was originally touted as being "lighter, less resource hungry and more energy-efficient", but now aims to be "a functional yet modular distribution focused on getting out of the way and letting users use their computer".

Lubuntu originally used the LXDE desktop, but moved to the LXQt desktop with the release of Lubuntu 18.10 in October 2018, due to the slow development of LXDE, losing support for GTK 2 as well as the more active and stable LXQt development without Gnome dependencies.

The name Lubuntu is a portmanteau of LXQt and Ubuntu. The LXQt name derives from the merger of the LXDE and Razor-qt projects, while the word Ubuntu means "humanity towards others" in the Zulu and Xhosa languages.

Lubuntu received official recognition as a formal member of the Ubuntu family on 11 May 2011, commencing with Lubuntu 11.10, which was released on 13 October 2011.

History
The LXDE desktop was first made available for Ubuntu in October 2008, with the release of Ubuntu 8.10 Intrepid Ibex. These early versions of Lubuntu, including 8.10, 9.04 and 9.10, were not available as separate ISO image downloads, and could only be installed on Ubuntu as separate lubuntu-desktop packages from the Ubuntu repositories. LXDE can also be retroactively installed in earlier Ubuntu versions.

In February 2009, Mark Shuttleworth invited the LXDE project to become a self-maintained project within the Ubuntu community, with the aim of leading to a dedicated new official Ubuntu derivative to be called Lubuntu.

In March 2009, the Lubuntu project was started on Launchpad by Mario Behling, including an early project logo. The project also established an official Ubuntu wiki project page, that includes listings of applications, packages, and components.

In August 2009, the first test ISO was released as a Live CD, with no installation option.

Initial testing in September 2009 by Linux Magazine reviewer Christopher Smart showed that Lubuntu's RAM usage was about half of that of Xubuntu and Ubuntu on a normal installation and desktop use, and two thirds less on live CD use.

In 2014, the project announced that the GTK+-based LXDE and Qt-based Razor-qt would be merging into the new Qt-based LXQt desktop and that Lubuntu would consequently be moving to LXQt. The transition was completed with the release of Lubuntu 18.10 in October 2018, the first regular release to employ the LXQt desktop.

During the 2018 transition to becoming LXQt-based, the aim of Lubuntu was re-thought by the development team. It had previously been intended for users with older computers, typically ten years old or newer, but with the introduction of Windows Vista PCs, older computers gained faster processors and much more RAM, and by 2018, ten-year-old computers remained much more capable than had been the case five years earlier. As a result, the Lubuntu development team, under Simon Quigley, decided to change the focus to emphasize a well-documented distribution, based on LXQt "to give users a functional yet modular experience", that is lightweight by default and available in any language. The developers also decided to stop recommending minimum system requirements after the 18.04 LTS release.