What is the Genesis Block?
The Genesis Block is the first block ever mined on the Bitcoin blockchain. Satoshi Nakamoto created it on January 3, 2009. Also called Block 0. Encoded inside it: a London Times headline from that morning, "Chancellor on brink of second bailout for banks." The first thing Bitcoin ever recorded was an editorial note about why it had to exist.
Why It Matters
Every block in the Bitcoin blockchain traces back to the Genesis Block through cryptographic hashing. It's the anchor. If you could rewrite the Genesis Block, you could rewrite all of Bitcoin. That no one can is why the chain holds together.
The embedded Times headline is not decoration. It dates the block to a specific moment in the 2008 financial crisis. Banks were being bailed out for the second time in months. Satoshi was writing the first block of an alternative monetary system and timestamped it against the failure of the existing one. The message was the thesis.
The 50 BTC reward in the Genesis Block can never be spent. A quirk in the original code (or possibly intentional) makes those coins forever unspendable. They sit in an address anyone can view and no one will ever move.
How It Works
The Genesis Block is block height 0, mined by Satoshi using the original Bitcoin software. Unlike every block after it, it has no previous block to reference. It is the chain's starting point.
It contains one coinbase transaction crediting 50 BTC to an address only Satoshi knows. The block's hash is 000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f. One hash. Every subsequent block cryptographically anchors to it.
You can view the Genesis Block on any blockchain explorer by searching for block 0 or that hash. The original timestamp, the embedded headline, the unspendable reward. Sixteen years of Bitcoin history sit on top of it.