An online auction (also electronic auction, e-auction, virtual auction, or eAuction) is an auction held over the internet and accessed by internet connected devices. Similar to in-person auctions, online auctions come in a variety of types, with different bidding and selling rules.

The e-commerce and online auction industry, measured by revenue, was $995.8 billion in 2023. eCommerce sales for businesses have been steadily increasing for years, and with the migration of virtually all transactions to digital due to the COVID Pandemic, worldwide sales through ecommerce sales channels such as websites and online marketplaces increased overall in 2020.

There are two primary markets for online auctions: business to business (B2B) and business to consumer (B2C). B2C is forecast to have over a 1% annual growth rate, achieving a nearly 22% share of total global retail sales by 2024. B2B ecommerce gross merchandise value showed a similarly steady rate through 2019, as to mirror its retail B2C counterpart.

The largest consumer-to-consumer online auction site is eBay, which researchers suggest is popular because it is a convenient, efficient, and effective method for buying and selling goods.

Despite the benefits of online auctions, the anonymity of the internet, the large market, and the ease of access makes online auction fraud easier than in traditional auctions. The FTC categorizes online auction fraud reports with online shopping categories.