Square Co., Ltd., also known under its international brand name SquareSoft, was a Japanese video game developer and publisher. It was founded in 1986 by Masafumi Miyamoto, who spun off the computer game software division of Den-Yu-Sha, a power line construction company owned by his father. Among its early employees were designers Hironobu Sakaguchi, Hiromichi Tanaka, Akitoshi Kawazu, Koichi Ishii, artist Kazuko Shibuya, programmer Nasir Gebelli, and composer Nobuo Uematsu. Initially focusing on action games, the team saw popular success with the role-playing video game Final Fantasy in 1987, which would lead to the franchise of the same name being one of its flagship franchises. Later notable staff included directors Yoshinori Kitase and Takashi Tokita, designer and writer Yasumi Matsuno, artists Tetsuya Nomura and Yusuke Naora, and composers Yoko Shimomura and Masashi Hamauzu.

Initially developing for PCs, then exclusively for Nintendo systems, Square cut ties with Nintendo in the 1990s to develop for Sony Computer Entertainment's upcoming console PlayStation. Their first major project for the console, Final Fantasy VII, was a worldwide critical and commercial success and was credited with boosting the popularity of role-playing video games and the PlayStation outside Japan. Alongside the Final Fantasy series, the company developed and published several other notable series, including SaGa, Mana, Front Mission, Chrono and Kingdom Hearts. Over the years, many staff left to found studios such as the still active Monolith Soft and Mistwalker, and the now defunct Sacnoth and AlphaDream.

In 2001, the company saw financial troubles due to the commercial failure of the feature film Final Fantasy: The Spirits Within, which ultimately led Sakaguchi to leave the company in 2003. The film's failure disrupted merger discussions with Enix, publisher of the Dragon Quest series. Following the success of Final Fantasy X and Kingdom Hearts, negotiations resumed and the merger went ahead on April 1, 2003, forming Square Enix.

Square was initially established in September 1983 as a software subsidiary of Den-Yu-Sha, an electric power conglomerate led by Kuniichi Miyamoto. His son Masafumi Miyamoto, then a part-time employee of the Science and Technology Department at Keio University, had little interest in following his father into the electricity business. Miyamoto instead became a software developer at the Yokohama branch of Den-Yu-Sha in Hiyoshi, with a focus on the emerging video game market. Their original offices were based in a former hairdresser's salon. The company's name referred to a golfing term, and represented its aim to face challenges head-on. It also referenced a town square, emphasizing a production environment based on cooperation.

At the time, video games in Japan were usually created by a single programmer. Miyamoto, on the other hand, believed that graphic designers, programmers, and professional story writers would be needed to keep up with advances in computing and video game development. During these early years, the group was compared to a family business; one of the early hires, Shinichiro Kajitani, joined because he was a friend of Miyamoto, and later compared the company at that time to a "college club". To recruit for this new organizational structure, Miyamoto organized a salon in Yokohama and offered jobs to those who demonstrated exceptional programming skills. This led to the part-time hiring of university students Hironobu Sakaguchi and Hiromichi Tanaka, as well as Hisashi Suzuki, who would go on to become Square's CEO. Miyamoto's initial plan was to recruit from Keio University, but this never materialized.

Square's first attempt at a game was an adaptation of the television game show Torin-ingen. As Miyamoto had not secured the license to adapt it, the show's producers forced Square to cancel the game, prompting its team to be reshuffled. Square's first completed game was The Death Trap (1984) for NEC PC-8801, a text adventure set in a war-torn African nation. The Death Trap was the first game published under the Square brand. Its sequel, Will: The Death Trap II, was released the following year to commercial success. Many of Square's early titles were produced for PC devices, and focused on the action genre.

In 1985, the company negotiated a licensing agreement with Nintendo to develop titles for the Family Computer. The company shifted to developing for the Famicom to benefit from its stable hardware, compared to the constantly changing components of PCs. Square's first Famicom release was a port of the run and gun game Thexder (1985), and its first original game was the scrolling shooter King's Knight (1986). During this period, the team also hired new developers Akitoshi Kawazu and Koichi Ishii, artist Kazuko Shibuya, Iranian-American programmer Nasir Gebelli, and composer Nobuo Uematsu. Yusuke Hirata joined that year as sales manager, and later became the company's publicity manager.

In April 1986, Square moved into new offices based in Ginza, noted as one of the most expensive areas for companies to operate; Sakaguchi later speculated Miyamoto was hoping to attract business by appearing affluent. Square was re-established as an independent developer in September of that year with capital of ¥10 million, buying the original Square gaming division from Den-Yu-Sha in December. Sakaguchi was appointed as a Director of Planning and Development, and Hisashi Suzuki became one of the company's directors. Due to the high cost of Ginza rents, the company was forced to move into smaller offices in Okachimachi, Taitō. Square began struggling financially following multiple commercial failures for Nintendo's Famicom Disk System peripheral. Miyamoto asked the company's four directors for game proposals, with plans to have their staff vote on the best idea. Sakaguchi proposed making a role-playing video game (RPG), believing it to be a viable project after the success of Enix's Dragon Quest (1986).