Genesis Block: the first block of a blockchain

Block Zero of a Blockchain

The genesis block is the very first block of a blockchain. Every subsequent block references the hash of the one before it, so the entire chain ultimately traces back to a single starting point. The genesis block has no predecessor, which is why it is typically hardcoded directly into the protocol's source code rather than being mined like a normal block.

Bitcoin's genesis block was created by Satoshi Nakamoto on January 3, 2009. It contains a famous embedded message in its coinbase parameter: "The Times 03/Jan/2009 Chancellor on brink of second bailout for banks." The phrase serves both as a timestamp and as a political statement, anchoring Bitcoin's launch to the financial crisis it was designed to challenge.

Unlike later blocks, Bitcoin's genesis block reward of 50 BTC is unspendable due to a quirk in the original code. Other blockchains have their own genesis blocks with their own histories—Ethereum's was generated in July 2015 and recorded the initial token distribution from its crowdsale. Because every full node validates the chain back to block zero, tampering with the genesis block would invalidate the entire network.