<p>All nodes (not just mining ones) maintain something called a mempool, a collection of all of the validated transactions they have seen on the network which have not made it into blocks so far. A miner is free to take all of them that will fit, a subset which satisfy their own requirements, or none of these transactions and assemble them into a candidate block. The block they assemble is invalid until they find proof of work that satisfies the current difficulty, if they find the correct nonce for that block it becomes valid and they can broadcast it to the network. If someone else finds a block before they do, the candidate block is discarded and a new one assembled to work against. </p>

CC BY-SA 3.0
2015-06-15T09:47:10.497Z
2015-06-15T09:47:10.497Z
Claris
<p>I am newbie in the Bitcoin field.</p>

<p>I have read about the transactions, blocks, blockchain and other materials.
As I know, when a new valid block is found and announced by a user, other users start working on the next block. But what is the mechanism of determining the transactions of the next block. I mean which transaction are going to form the new next block? Is that all transaction broadcasted before the announcing of the last valid block?</p>

<p>Thanks in advance!</p>

CC BY-SA 3.0
2015-06-15T14:13:37.560Z
possible duplicate: [How do miners select which transactions to include in a block?](http://bitcoin.stackexchange.com/q/7311/5406)
Murch
<transactions><blockchain><block>
What is the mechanism of determining the transactions of a new block
Tail of Godzilla
# What is the mechanism of determining the transactions of a new block

(Asked by: username_0 on 2015-06-15)

I am newbie in the Bitcoin field.

I have read about the transactions, blocks, blockchain and other materials.
As I know, when a new valid block is found and announced by a user, other users start working on the next block. But what is the mechanism of determining the transactions of the next block. I mean which transaction are going to form the new next block? Is that all transaction broadcasted before the announcing of the last valid block?

Thanks in advance!

**Tags:** transactions, blockchain, block

> **Comments:**
> **username_1**: possible duplicate: [How do miners select which transactions to include in a block?](http://bitcoin.stackexchange.com/q/7311/5406)  

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## 1 answers

### Answer by username_2 on 2015-06-15. Score: 0 | Accepted answer

All nodes (not just mining ones) maintain something called a mempool, a collection of all of the validated transactions they have seen on the network which have not made it into blocks so far. A miner is free to take all of them that will fit, a subset which satisfy their own requirements, or none of these transactions and assemble them into a candidate block. The block they assemble is invalid until they find proof of work that satisfies the current difficulty, if they find the correct nonce for that block it becomes valid and they can broadcast it to the network. If someone else finds a block before they do, the candidate block is discarded and a new one assembled to work against.


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