The coinbase transaction is a special and unique transaction included in every block of the Bitcoin blockchain. It represents the first transaction of a block and is created by the miner who has successfully found a header validating the proof of work (Proof-of-Work), that is, less than or equal to the target.

The coinbase transaction primarily serves two purposes: to award the block reward to the miner and to add new units of bitcoins to the circulating money supply. The block reward, which is the economic incentive for miners to engage in proof of work, includes the accumulated fees for the transactions included in the block and a determined amount of newly created bitcoins ex-nihilo (block subsidy). This amount, initially set at 50 bitcoins per block in 2009, is halved every 210,000 blocks (approximately every 4 years) during an event called "halving."

The coinbase transaction differs from regular transactions in several ways. First, it does not have an input, meaning no existing transaction output (UTXO) is consumed by it. Next, the signature script (scriptSig) for the coinbase transaction typically contains an arbitrary field allowing for the incorporation of additional data, such as custom messages or mining software version information. Finally, the bitcoins generated by the coinbase transaction are subject to a maturity period of 100 blocks (101 confirmations) before they can be spent, to prevent the potential spending of non-existent bitcoins in case of a chain reorganization.