HistoryDesignEthereum is a permissionless, non-hierarchical network of computers (nodes) which build and come to consensus on an ever-growing series of blocks, or batches of transactions, known as the blockchain. Each block contains an identifier of the block that it must immediately follow in the chain if it is to be considered valid. Whenever a node adds a block to its chain, it executes the transactions therein in their order, thereby altering the ETH balances and other storage values of Ethereum accounts. These balances and values, collectively known as the state, are maintained on the nodes computer separately from the blockchain, in a Merkle Patricia tree. Each node communicates with a relatively small subset of the network, known as its peers. Whenever a node wishes to include a new transaction in the blockchain, it sends it to its peers, who then send it to their peers, and so on. In this way, it propagates throughout the network. Certain nodes, called miners, maintain a list of all of these new transactions and use them to create new blocks, which they then send to the rest of the network. Whenever a node receives a block, it checks the validity of the block and of all of the transactions therein and, if valid, adds it to its blockchain and executes all of said transactions. As the network is non-hierarchical, a node may receive competing blocks, which may form competing chains. The network comes to consensus on the blockchain by following the longest chain rule, which states that the chain with the most blocks at any given time is the canonical chain. This rule achieves consensus because miners do not want to expend their computational work trying to add blocks to a chain that will be abandoned by the network. Ether Ether (ETH) is the cryptocurrency generated by the Ethereum protocol as a reward to miners in a proof of work system for adding blocks to the blockchain. It is the only currency accepted in the payment of transaction fees, which also go to miners. The terms Ether and Ethereum have become interchangeable in the cryptocurrency community.