Payment Channel

A payment channel is the foundational building block of the Lightning Network. Two parties open a channel by broadcasting a single on-chain funding transaction that locks Bitcoin into a 2-of-2 multisignature output controlled by both keys. Once confirmed, the pair can exchange an effectively unlimited number of payments off-chain by re-signing the channel's balance, settling on the Bitcoin blockchain only when they choose to close.

Commitment transactions and balance updates

The current split of funds is recorded in a pair of commitment transactions, each signed by the counterparty. To send value, the parties simply sign a new commitment reflecting the updated balance. No miner ever sees these intermediate states, which is why Lightning payments are near-instant and cost a fraction of an on-chain fee.

Revocation keeps old states honest

Because every past commitment remains technically valid, the protocol uses a revocation mechanism: before adopting a new state, each party hands over the secret needed to punish them if they ever broadcast the old one. If a cheater publishes a stale commitment, the honest party can sweep the entire channel balance using a penalty (justice) transaction. This trust-minimized design, descended from the Poon-Dryja construction, is what lets Lightning scale Bitcoin without custodians.

Closing: the graceful way and the hard way

A channel ends in one of two ways. A cooperative close has both parties sign a final settlement transaction paying each side its current balance immediately — cheap, fast, and the normal case. A force close is the unilateral escape hatch: one party broadcasts the latest commitment transaction on its own, which works even if the counterparty has vanished, but at a price — the closer's funds are locked behind a timelock delay, giving the other side its window to submit a penalty transaction if the broadcast state was stale. This asymmetry is deliberate: the channel is designed so that honesty is always the cheaper strategy, and abandonment by a peer can never trap your coins permanently. It is also why a Lightning node must stay online or delegate a watchtower — someone has to be watching the chain for stale broadcasts during that window.

Liquidity: the dimension newcomers miss

A channel's funds are split into outbound capacity (what you can send) and inbound capacity (what you can receive), and every payment shifts the balance point between them. A freshly opened channel funded entirely by you can send but not receive; earning inbound capacity means spending, being paid, or arranging channels funded toward you. Since a single payment cannot exceed what the channels along its route can carry, capacity planning — how much, with whom, in which direction — is the real operational craft of running Lightning, covered further under channel capacity. On-chain fees frame the economics of it all: opening and closing each cost a transaction, so a channel makes sense when the value of the payments it will carry comfortably exceeds its setup cost — which is exactly why channels suit recurring relationships and routing nodes better than one-off payments, and why fee spikes on the base layer ripple into Lightning as costlier channel management.

Why it matters for sovereignty

Payment channels are what let a self-hosted Bitcoin stack scale to everyday payments without surrendering custody: your node, your channels, your keys, with the blockchain as the court of final settlement rather than the rail for every coffee. Running your own Lightning node on the same hardware as your full node keeps the entire payment path under your control.

Channels are the medium through which HTLCs route multi-hop payments. To understand how funds become spendable in both directions, see channel capacity.