Sony Mobile Communications Inc., originally Sony Ericsson Mobile Communications AB, was a multinational consumer electronics and telecommunications company, best known for its mobile phone products. The company, originally a joint venture between Sony and Ericsson, marketed products under the "Sony Ericsson" brand from 2001 until 2012, when Ericsson sold its share to Sony, with products hereafter being branded as "Sony". As part of a corporate restructuring, Sony Mobile was superseded by and integrated into Sony Corporation in 2021.

The alliance between Swedish telecom giant Ericsson and Japanese electronics giant Sony was formed to benefit Ericsson Mobile recover against competitors in the mobile phone market, while for Sony it gave the opportunity to grow in the field of cellular communication, where it had only a minor presence. Products and development was done with contributions from both parties: the company itself was based in London, England, with its design centre in Lund, Sweden, and other research and development facilities in Beijing, China; Tokyo, Japan; and San Francisco, United States. The Sony Ericsson T68i was the first GSM phone released under the joint venture since its launch. After the Sony acquisition, the company, now as Sony Mobile, moved its headquarters to Tokyo, Japan.

Some of the most notable phones produced by Sony Ericsson include the T610, the K800i (Cyber-shot branded), the W810 (Walkman-branded), and the Xperia arc S. Sony Ericsson was also the main user of the UIQ smartphone platform, but beginning in 2010 had switched over entirely to Android. After the end of the joint venture, the Xperia sub-brand of Android smartphones would be the only handsets under the Sony brand, although Sony Mobile also developed tablet computers (Xperia Tablet), smartwatches (Sony SmartWatch) and fitness trackers (Sony SmartBand).

At its peak in 2007, Sony Ericsson, Sony Mobile's predecessor, held a 9 percent global mobile phone market share making it the fourth largest vendor at the time. In 2017, Sony Mobile held less than 1% global market share but 4.8% in Europe and 16.3% in Japan.

The Swedish company Ericsson had been making mobile cell phones since the 1980s, with their very first handheld device being the Hotline Pocket introduced in 1987. In the United States, Ericsson partnered with General Electric in the early nineties as Ericsson Mobile Communications (ECS), primarily to establish a US presence and brand recognition. General Electric eventually left the joint venture.

Ericsson had decided to obtain chips for its phones from a single source—a Philips facility in New Mexico. On March 17, 2000, a fire at the Philips factory contaminated the sterile facility. Philips assured Ericsson and Nokia (their other major customer) that production would be delayed for no more than a week. When it became clear that production would actually be compromised for months, Ericsson was faced with a serious shortage. Nokia had already begun to obtain parts from alternative sources, but Ericsson's position was much worse as production of current models and the launch of new ones was held up.

Ericsson, which had been in the mobile phone market for decades, and was the world's third largest cellular telephone handset maker at the time behind Nokia and Motorola, was struggling with huge losses and decreasing market share. This was partly due to this fire as well as its inability to produce cheaper phones or fashionably-designed phones like Nokia managed to do. Speculation began about a possible sale by Ericsson of its mobile phone division, but the company's president, Kurt Hellström, said it had no plans to do so. Hellström said, "Mobile phones are really a core business for Ericsson. We wouldn't be as successful (in networks) if we didn't have phones".

Sony was a marginal player in the worldwide mobile phone market with a share of less than 1 percent in 2000. By August 2001, the two companies had finalised the terms of the merger announced in April. Ericsson contributed a majority of the Ericsson Mobile Communications company, excluding a minor part spun off as Ericsson Mobile Platforms. Sony contributed its entire handset division. The company was to have an initial workforce of 3,500 employees.