Mecha, also known as giant robot or simply robot, is a genre of anime and manga that feature mecha in battle. The genre is broken down into two subcategories; "super robot", featuring super-sized, implausible robots, and "real robot", where robots are governed by realistic physics and technological limitations.

Mecha series cover a wide variety of genres, from action to comedy to drama, and the genre has expanded into other media, such as video game adaptations. Mecha has also contributed to the popularity of scale model robots.

The 1940 short manga Electric Octopus (デンキダコ, Denki Dako) featured a powered, piloted, mechanical octopus. The 1943 Yokoyama Ryūichi's propaganda manga The Science Warrior Appears in New York (科学戦士ニューヨークに出現す, Kagaku Senshi New York ni Shutsugensu) featured a sword-wielding, steam-powered, giant humanoid mecha.

The first series in the mecha genre was Mitsuteru Yokoyama's 1956 manga Tetsujin 28, which was also released as an anime in 1963. Yokoyama was inspired to become a manga creator by Osamu Tezuka, and began serializing the manga in Shonen, an iconic boy's magazine, in 1956. In this series, the robot, which was made as a last-ditch effort to win World War II by the Japanese military, was remote-controlled by the protagonist Shotaro Kaneda, a twelve-year-old detective and "whiz kid". The story turned out to have immense mass appeal, and inspired generations of imitators.

In 1972, Go Nagai defined the super robot genre with Mazinger Z, which was directly inspired by the former series. He had the idea to create a mecha that people could control like a car, while waiting to cross a busy street. The concept became "explosively popular", making the manga and anime into a success. The series also was the genesis for different tropes of the genre, such as the idea of a robot as a "dynamic entity" that could join with other machines or humans to become unstoppable. Anime critic Fred Patten wrote that almost all mecha anime plots, such as monster of the week shows, were actually metaphors for re-fighting World War II, and defending Japan and its culture from Western encroachment.

By 1977, a large number of super robot anime had been created, including Brave Raideen and Danguard Ace. The market for super robot toys also grew, spawning metal die-cast toys such as the Chogokin series in Japan and the Shogun Warriors in the U.S., that were (and still are) very popular with children and collectors. The super robot genre became heavily commercialized and stagnant, creating an opening for innovation, which was seized upon by Yoshiyuki Tomino in 1979 with the creation of Mobile Suit Gundam, a complex "space saga" that was called the "Star Wars of Japan" and birthed the real robot genre, which featured more realistic, gritty technology. Tomino did not like the formulaic storylines and overt advertising of the super robot shows he had worked on, and wanted to create a movie where robots were used as tools. While the response to Gundam was lukewarm at first, efforts by dedicated fans led to it becoming a success. It created a massive market for mecha model robots, and became an industry that earned Bandai ¥42.8 billion in 2004. Many real robot series and other media were later created, such as Full Metal Panic! and the video game series Armored Core.

1990 saw the release of Patlabor, an animated movie directed by Mamoru Oshii that popularized the mecha genre and aesthetic in the West. Neon Genesis Evangelion, created by Hideaki Anno in 1995, was a major influence on the super robot genre, arriving when the real robot genre was dominant on television. Due to its unusual psychological themes, the show became a massive success, and further caused Japanese anime culture to spread widely and rapidly around the world.

The mecha anime genre (as well as Japanese kaiju films) received a Western homage with the 2013 film Pacific Rim directed by Guillermo del Toro. Similarly the genre was inspirational for the 1998 first-person shooter Shogo: Mobile Armor Division developed by Monolith Productions.