Lubuntu (/lʊˈbʊntuː/ luu-BUUN-too) is a lightweight Linux distribution based on Ubuntu that uses the LXQt desktop environment in place of GNOME. 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.

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.