Bisq is software, not a service. Two people run it on their own machines, find each other over a peer-to-peer network, and trade. There is no account, no deposit address belonging to an operator, and nothing to sign up for. The project's own description is "a decentralized bitcoin exchange network", and it notes you can start "without approval from a central authority".
The project began as Bitsquare. Chris Beams announced version 0.1 on 16 December 2014, after what the post calls "many months of research and development" and a pre-alpha period before that. In March 2017 Manfred Karrer published the rename: "we started rebranding as a result of trademark conflicts", and the replacement name was chosen partly because "it is not possible to use anything which even sounds similar to 'square'".
The mechanism that makes trading without a custodian work is a multi-signature escrow plus a security deposit from both sides, with human arbitration when a trade goes wrong. The code is licensed AGPL-3.0. Governance and funding run through a separate on-chain layer listed here as the Bisq DAO, and Bisq's own material states the arrangement bluntly: it operates "without any banks, corporations, or other legal entities". That is why this entry is marked unincorporated rather than undocumented. There is no company to sue, and no company to protect you either.
That tradeoff was tested in public. On 1 May 2026 an attacker used a modified client against missing validation checks in the Bisq v1 trade protocol, manipulating miner fee values. Ten users were affected and losses came to 11.59104 BTC, concentrated in three traders. Fiat trades and Bisq 2 were not affected. The team halted trading through emergency version enforcement, shipped v1.10.0 with wider protocol validation and a reduced trade size limit of 0.125 BTC, and submitted a reimbursement proposal to the DAO with the stated goal of repaying affected users in full.