Shein (/ˈʃiːɪn/ ^ⓘ SHEE-in; styled as SHEIN; Chinese: 希音; pinyin: Xīyīn) is a global e-commerce platform specializing in fast fashion. While the company primarily focuses on women's clothing, it also offers men's apparel, children's wear, accessories, cosmetics, shoes, bags, and other fashion items. Shein mainly focuses on Europe, America, Australia, and the Middle East along with other consumer markets worldwide.

Founded in Nanjing, China, in October 2008 as ZZKKO by entrepreneur Chris Xu, Shein grew to become the world's largest fashion retailer as of 2022. The company is currently headquartered in Singapore.

Known for selling relatively inexpensive apparel, Shein's success has been credited to its popularity among younger Millennial and older Generation Z consumers. The company was initially compared to a drop shipping business, as it was not involved in design and manufacturing, instead sourcing products from the wholesale clothing market in Guangzhou. Beginning in 2012, Shein began to establish its own supply chain system, transforming itself into a fully integrated retailer. The company has established its supply chain in Guangzhou with a network of more than 3,000 suppliers as of 2022. However, it has faced controversy due to the reports of Chinese sweatshops and child labor.

In 2022, the company moved its headquarters from China to Singapore for regulatory, international expansion, and financial reasons – while keeping its supply chains and warehouses in China. In 2023, Shein generated US$32 billion in revenue. Shein was valued at $100 billion after a funding round in April 2022. As of February 2025^[update], it was valued at $30 billion.

According to Bloomberg Businessweek and others, Shein's business model has benefitted from the China–United States trade war, particularly with regard to customs tax advantages. In recent years, Shein has found itself in the middle of trademark disputes, lawsuits involving competitors, and product safety concerns, as well as accusations of tax evasion and being involved in labor law and human rights violations.

Shein, originally named ZZKKO, was founded in China in 2008 by entrepreneur and search engine optimization (SEO) marketing specialist Chris Xu (Xu Yangtian). Information on Xu's educational and career background remains elusive as of 2022, with sources conflicting on details of his biography. According to The Guardian, some sources have described him as a Chinese-American who graduated from George Washington University (GWU). However, other sources indicate that Xu was born in 1984 in Shandong province, and was educated at Qingdao University of Science and Technology. The Guardian notes that Xu is depicted in Chinese media coverage as an average student of poor origins. Shein has insisted that Xu was born in China.

The website SheInside.com was registered in March 2011, advertising itself as "a worldwide leading wedding dress company", although it sold general womenswear as well.

At the time, Shein had no involvement in the design or production of the garments; it functioned similarly to a drop shipping firm, which sells items from third-party wholesalers directly to international customers.