OpenSea is a decentralized marketplace for non-fungible tokens (NFTs), founded in late 2017 by Devin Finzer and Alex Atallah. Built initially on Ethereum, it enables users to mint, buy, sell, and trade unique digital assets such as art, domain names, music, collectibles, virtual real estate, and utility tokens, all directly via smart contracts. OpenSea is non-custodial, meaning users retain full control of their assets through crypto wallets like MetaMask or Coinbase Wallet.

What sets OpenSea apart is its broad support across multiple blockchains and its peer-to-peer model. Originally rooted in Ethereum's ERC-721 and ERC-1155 token standards, OpenSea has since expanded to support Polygon, Solana, and others. It operates similarly to platforms like eBay or Etsy but for NFTs, allowing fixed-price listings, auctions, and off-chain offers, with transactions settled using smart contracts. OpenSea charges a standard secondary-sale fee of around 2.5 percent per transaction.

Over time, OpenSea has grown to become the world’s largest and most influential NFT marketplace. It has hosted millions of NFTs and reached unicorn status via multiple funding rounds, valued at over 13 billion dollars by early 2022. Despite encountering regulatory scrutiny, platform competition, and internal challenges in recent years, OpenSea continues iterating on its platform through efforts like its "OpenSea 2.0" initiative to improve discovery, usability, and cross-chain support while striving to remain a trusted and inclusive destination for creators and collectors alike.