Scion was a marque of Toyota that debuted in 2003 and was available only in the United States and Canada. The marque was intended to appeal to younger customers: the Scion brand emphasized inexpensive, stylish, and distinctive sport compact vehicles, and used a simplified "pure price" sales concept that eschewed traditional trim levels and dealer haggling. Each vehicle was offered in a single trim with a non-negotiable base price, while a range of dealer-installed options was offered to buyers for personalizing their vehicles. The Scion name, meaning the descendant of a family or heir, refers both to the brand's cars and their owners. In an effort to target millennials, Scion primarily relied on guerrilla and viral marketing techniques.

The brand first soft launched in the United States at selected Toyota dealers in the state of California in June 2003, before expanding nationwide by February 2004. Sales peaked in 2006 with 173,034 units sold. In 2010, Scion expanded into Canada. However, Toyota's initial propositions of short product cycles and aggressive pricing based on low dealer margins became increasingly unsustainable as sales fell after the 2008 financial crisis. Toyota abolished the Scion brand at the start of the 2017 model year in August 2016; the vehicles were either rebranded as Toyotas or discontinued.

In 1999, Toyota launched Project Genesis, an effort to bring younger buyers to the Toyota marque in the United States. This project aimed to create a "marque within a marque" in sales and advertising strategy for compact and coupe models sold by Toyota. The effort, which included the introduction of the Toyota Echo economy car, along with late generation Toyota MR-2 and Toyota Celica models, was judged unsuccessful and cancelled in 2001. In response, Toyota chose to launch a separate marque, an effort called Project Exodus. A Los Angeles-based digital design company, Fresh Machine, was retained by Toyota to develop the brand, logo, and website. This project became known as Scion. Toyota had previously participated in a project in Japan with other Japanese companies who attempted to market products to younger buyers. Toyota manufactured three vehicles under the WiLL brandname, which were exclusive to Toyota Netz Store Japanese dealerships.

Scion was marketed as a youth brand and was first introduced in March 2002, at the New York Auto Show. There were just two concept vehicles, the bbX (which became the xB), and the ccX (which became the tC). The 2004 xA and xB were unveiled at the Greater Los Angeles Auto Show on January 2, 2003. They were available only in 105 Toyota dealerships in California at their initial launch on June 9, 2003. The subsequent rollout of the brand to the South, the Southeast, and the East Coast occurred in February 2004. Scion vehicles were available nationwide in June 2004, coinciding with the release of the 2005 tC. On December 16, 2006, Scion unveiled the next-generation xB, based on the t2B concept, and the new xD, successor of the xA, at an invitation-only, no-camera event in Miami. Both cars were then publicly unveiled on February 8, 2007, at the Chicago Auto Show. The xD, a five-door subcompact car that is sold in Japan as the second generation Toyota Ist, was based on the Yaris platform with the tenth-generation Corolla's engine.

In September 2010, Scion expanded into Canada, with vehicles offered at 45 selected dealers starting in Toronto, Montreal, and Vancouver, followed by other cities. Launch models included the tC, xD, and xB. The first new Scions were shown in Canada at the 2009 Montreal International Auto Show.

Sales of the Scion brand were down to a low of 45,678 for the 2010 model year, compared to over 170,000 for 2006. The management tried to resuscitate the brand, hoping to sell 35,000 to 45,000 tC in a year after the model was redesigned for 2011. In October 2011, the iQ, an ultra-compact city car, debuted as a 2012 model. In April 2012, Jack Hollis (Vice President of Scion) announced that the xB and xD would be dropped after 2012, supposedly in favor of all new models from Toyota's hatchback division, Daihatsu; the same month, the FR-S sports car went on sale as a 2013 model. Later in 2012—despite the announcement of its imminent discontinuation—a facelifted version of the xB was unveiled.

In late 2013, the xD and second-generation xB were in their seventh year without a substantial redesign, and Scion sales were still far short of their 2006 peak. Toyota began allowing dealers to drop the Scion marque without penalty. The recently introduced FR-S had strong initial sales, but combined sales of the new FR-S and redesigned tC did not equal sales of the tC alone during 2005 through 2008, and industry observers concluded that the FR-S was cannibalizing sales of the similar tC. iQ sales never met expectations, and by 2014, observers were characterizing it as a "disappointment." A primary goal of the Scion brand was to introduce young first-time buyers to Toyota products, but analysts found that relatively few Scion buyers were making follow-on purchases from the more profitable Toyota and Lexus lines, and Gen Y buyers were generally making more pragmatic car-buying choices than their predecessors due to economic factors.

For the 2015 model year, Scion released the iM hatchback, based on the international Toyota Auris, and the iQ, xB, and xD were discontinued. Scion also introduced the iA sedan, a rebadged version of the Mazda2; however, Toyota opted to sell the iA as the Toyota Yaris sedan in Canada.