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Blocks & network · 2 min read

What is a genesis block?

By Oliver James Whitmore · Updated 20 October 2026

In one sentence

The genesis block is the first block of a blockchain — block number zero — which has no parent and is written directly into the network's software instead of being produced by consensus.

Bitcoin from paper to first blocks: the whitepaper, the genesis block, block 1 and block 170.31 Oct 2008whitepaper3 Jan 2009block 0 (genesis)9 Jan 2009block 112 Jan 2009block 170Block 170 is generally cited as the first transfer between two people
Bitcoin from paper to first blocks: the whitepaper, the genesis block, block 1 and block 170.

How it works

Every block points to the one before it, except the first. Since there is nothing to point to, the genesis block is defined by hand: its contents and hash are written into the source code of every node. All nodes start from this agreed anchor, and every later block can be traced back to it.

Bitcoin's genesis block carries the timestamp 3 January 2009. The text embedded in its first transaction quotes a newspaper headline from that day: "Chancellor on brink of second bailout for banks", from The Times. It is usually read in two ways: as evidence that the block was not created before that date, and as a comment on the banking crisis of the time. The 50 new units in that transaction cannot be spent, because of the way the software handles the genesis block. The next block, number 1, was mined on 9 January 2009.

Ethereum's genesis block dates from 30 July 2015, the launch of its first live release, Frontier. Unlike Bitcoin's, it already assigned balances to many addresses, reflecting a sale of ether that took place in 2014.

Test networks and private chains each have their own genesis block. That is one simple way networks are kept apart.

A simple example

Two nodes run the same software version but have been given different genesis blocks. When they connect, they cannot agree on even the first block, so they cannot follow the same chain. Changing the genesis block, in effect, creates a different network.

Common misconception

Misconception: The genesis block contains the first payment from one person to another.

In fact: The genesis block only created new units, and those can never be moved. The first transfer between two people on Bitcoin is generally dated to block 170, on 12 January 2009.

Where you meet it

  • "Block 0" or "height 0" in any block explorer.
  • The configuration of test networks and private chains.
  • The source code of node software, where its hash is written down as a fixed constant.
  • Histories of Bitcoin, alongside the whitepaper of 31 October 2008.

Sources

This card explains a technical concept for general education. It is not a recommendation to acquire, sell or hold any crypto-asset, and it is not financial advice.