<p>David has already given a good explanation of the term coinbase, but I'd like to give further details on the <strong>coinbase transaction</strong>.</p>

<p>The <em>coinbase transaction</em> is a special type of transaction. </p>

<ul>
<li>Every block must have a coinbase transaction, <a href="https://bitcoin.stackexchange.com/q/2021/5406">other transactions are optional</a>.</li>
<li>The coinbase transaction must be the first transaction of the block (it follows that there can only be one per block).</li>
<li>The coinbase's output is used to send the block reward, i.e. block subsidy plus transaction fees, to the miner's address.</li>
<li>The coinbase transaction can have an arbitrary input of 100 byte size. E.g. this was where the genesis block famously contained "The Times 03/Jan/2009 Chancellor on brink of second bailout for banks". This is also the field that may be used for the <a href="https://bitcoin.stackexchange.com/q/5048/5406"><code>extranonce</code></a>.</li>
</ul>

CC BY-SA 3.0
2016-06-27T13:12:23.567Z
2016-06-27T13:12:23.567Z
2017-04-13T12:47:34.187Z
Murch
<p>The term "coinbase" is used to mean many different things. But the two you're probably asking about are:</p>

<ol>
<li><p>The "coinbase transaction" is the transaction inside a block that pays the miner his block reward.</p></li>
<li><p>Inside the coinbase transaction is a field that is called the "coinbase". It's the <a href="https://en.bitcoin.it/wiki/Transactions#Generation">generation transaction's</a> equivalent of a scriptsig. Since it doesn't claim any existing outputs, it needs no normal scriptsig. It's basically just a random value that the miner can use as an additional nonce. <a href="https://en.bitcoin.it/wiki/BIP_0034">BIP 34</a> changes this a bit.</p></li>
</ol>

CC BY-SA 3.0
2013-02-21T04:25:17.220Z
There's also now a Bitcoin exchange/hosted wallet web site called http://www.coinbase.com.
gosmond
CC BY-SA 3.0
2012-08-27T23:11:52.103Z
2012-08-27T23:11:52.103Z
David Schwartz
<p>I searched the bitcoin wiki and found references to coinbase, but no clear cut explanation of what exactly it is.  I know that miners can tag their coinbases (that is how some sites tell who mined a block).</p>

CC BY-SA 3.0
2012-11-26T05:12:14.550Z
Not to be confused with the Bitcoin startup Coinbase, which is a hosted (shared) EWallet + exchange.
Stephen Gornick
CC BY-SA 3.0
2015-11-07T15:20:15.127Z
For questions about the company see the tag [tag:coinbase.com].
Murch
<protocol><mining-reward><coinbase-transaction>
What is the coinbase?
Andrew Burns
# What is the coinbase?

(Asked by: username_0 on 2012-08-27)

I searched the bitcoin wiki and found references to coinbase, but no clear cut explanation of what exactly it is. I know that miners can tag their coinbases (that is how some sites tell who mined a block).

**Tags:** protocol, mining-reward, coinbase-transaction

> **Comments:**
> **username_1**: Not to be confused with the Bitcoin startup Coinbase, which is a hosted (shared) EWallet + exchange.  
> **username_2**: For questions about the company see the tag [tag:coinbase.com].  

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## 2 answers

### Answer by username_3 on 2012-08-27. Score: 32

The term "coinbase" is used to mean many different things. But the two you're probably asking about are:

1. The "coinbase transaction" is the transaction inside a block that pays the miner his block reward.
2. Inside the coinbase transaction is a field that is called the "coinbase". It's the [generation transaction's](https://en.bitcoin.it/wiki/Transactions#Generation) equivalent of a scriptsig. Since it doesn't claim any existing outputs, it needs no normal scriptsig. It's basically just a random value that the miner can use as an additional nonce. [BIP 34](https://en.bitcoin.it/wiki/BIP_0034) changes this a bit.

> **Comments:**
> **username_4**: There's also now a Bitcoin exchange/hosted wallet web site called http://www.coinbase.com.  

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### Answer by username_2 on 2016-06-27. Score: 11

username_3 has already given a good explanation of the term coinbase, but I'd like to give further details on the **coinbase transaction**.

The *coinbase transaction* is a special type of transaction.

* Every block must have a coinbase transaction, [other transactions are optional](https://bitcoin.stackexchange.com/q/2021/5406).
* The coinbase transaction must be the first transaction of the block (it follows that there can only be one per block).
* The coinbase's output is used to send the block reward, i.e. block subsidy plus transaction fees, to the miner's address.
* The coinbase transaction can have an arbitrary input of 100 byte size. E.g. this was where the genesis block famously contained "The Times 03/Jan/2009 Chancellor on brink of second bailout for banks". This is also the field that may be used for the [`extranonce`](https://bitcoin.stackexchange.com/q/5048/5406).


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