BIP 39 — Mnemonic code for generating deterministic keys

BIP 39 (Mnemonic code for generating deterministic keys) specifies how random entropy maps to a human-readable mnemonic (commonly 12 or 24 words from a 2048-word list) and how that mnemonic, optionally with a passphrase, is stretched into a seed for BIP 32 derivation. Repository status: Deployed.

Debate relevance: The 'seed phrase' in virtually every self-custody debate. Backup practices, passphrase ('25th word') tradeoffs, and vendor deviations from the standard all reference it. Common misstatements: "The seed phrase is my private key" — it is material from which keys are derived, together with derivation paths. "BIP 39 was never accepted" — older databases list it as 'Proposed' under the pre-2025 status system; current repository status is Deployed. Also, words alone may not suffice for recovery if a wallet used nonstandard derivation (see BIP 380 descriptors).