Amazon remains the dominant U.S. marketplace, with an estimated $300 billion in third-party sales, more than seven times eBay’s and roughly 20 times that of the next competitors. Three platforms – Temu, TikTok Shop, and Walmart – now compete in a tight $15-22 billion range, while specialized marketplaces from Wayfair to Whatnot have carved defensible positions serving niches that mass-market platforms struggle to capture.Two years ago, Temu targeted $24 billion in U.S. GMV for 2024. It hit an estimated $22 billion in 2025. TikTok Shop reached $15 billion in GMV, as did Walmart. Three fundamentally different business models – Temu’s supply chain arbitrage, TikTok’s content-first discovery, Walmart’s physical retail integration – all settled into the same narrow competitive band.Amazon’s CEO, Andy Jassy, recently claimed Rufus, its AI shopping assistant, drove $12 billion in incremental sales in 2025. If just half of those sales occurred in the U.S., Rufus alone would rank as the seventh-largest marketplace in the country – tied with SHEIN, Etsy, and Whatnot at $6 billion. Similarly, Amazon Haul, its direct-from-China storefront launched to compete with Temu, already spans over one million items under $10 across 25 markets, and generates an estimated $2 billion in the U.S. Amazon’s experiments operate at the scale of entire companies.eBay holds second position at $39 billion after returning to growth by refocusing on enthusiasts and pre-loved fashion rather than competing for new-in-season goods it acknowledged it couldn’t win. The platform accepted a ceiling in exchange for stability, carving out a defensible position Amazon doesn’t particularly want.Temu’s $22 billion defies clean categorization. While classified as marketplace GMV, the platform operates across a spectrum from full consignment where Temu controls pricing to semi-managed programs where sellers manage local inventory. The forced shift from direct-from-China to domestic fulfillment following de minimis suspension accelerated the business model evolution. The platform now aggressively recruits sellers with registration incentives and infrastructure support, pushing toward a traditional marketplace structure even as it retains pricing control over significant portions of its catalog. It’s neither pure retailer nor pure marketplace – it’s both.TikTok Shop and Walmart are tied at $15 billion, arriving through opposite paths. TikTok Shop grew 68% year-over-year despite regulatory chaos and now mostly resolved ownership uncertainty. Walmart grew from $10 billion while crossing 200,000 sellers, but its evolution follows a familiar pattern with advertising revenue growing six times faster than sales.Shopify doesn’t feature as it is neither a marketplace nor a retailer. However, it now claims 14% of U.S. e-commerce, and its global GMV reached 66% of Amazon’s marketplace GMV in 2025, up from 40% in 2020. If Shopify’s millions of merchant storefronts were treated as a single marketplace, it would rank second only to Amazon. Instead, it represents the decentralized alternative – merchants own their storefronts, their customer relationships, and their brand identity, selling directly rather than through centralized discovery.Beyond the top five, five more platforms have built billion-dollar marketplaces: Wayfair at $10 billion in home goods, SHEIN’s marketplace at $6 billion (24% of U.S. GMV), Etsy at $6 billion in handmade goods, Whatnot at $6 billion in live auctions, and Target Plus at $1 billion with its curated model. The marketplace economy is bigger and more diverse than ever.