Buy and sell bitcoin for fiat (or other cryptocurrencies) privately and securely using Bisq's peer-to-peer network and open-source desktop software. No registration is required. Bisq is a peer-to-peer trading network, not a website or "app" or another centralized service. It's software you run on your own hardware, which connects to other people running the Bisq software to facilitate trades. It's open-source and community-driven.
