 Sudakar asks, what will metropolis mean for Ethereum? Great question, Sudakar. Metropolis is the third out of the four plant transitions for Ethereum. Ethereum was deployed in a manner that expects that there will be certain major transitions... between different stages of development. The first stage of development for Ethereum was called Frontier. Frontier was the stage of development that involved the pre-sell of Ethereum. The first, essentially, pre-beta version of Ethereum ran on the network. The current version of Ethereum was the current stage of Ethereum, called Homestead. Homestead is planned to end in the next year. We will transition to the third stage of Ethereum, called Metropolis. It is also named in advance, the final stage of Ethereum, which will be the stage that Ethereum settles in. It will be called Serenity. Frontier, Homestead, Metropolis, and Serenity are the four evolutionary stages of Ethereum. Metropolis was actually planned for 2017, or perhaps the end of 2016. But because of the Dow incident, the fork to classic, several denial-of-service attacks, and other problems that occurred during Homestead, instead the developers were delayed and distracted, fixing security problems, and doing a number of hard forks to address certain vulnerabilities discovered in Homestead. As a result, Metropolis has been delayed, but it is expected in 2018, and it is moving pretty fast now. Metropolis introduces a number of different changes to Ethereum, and it is going to happen in two stages, which are codenamed Byzantium and Constantinople. Byzantium is the first stage of Metropolis, and Constantinople is the second stage of Metropolis. Each of those will be a hard fork, or perhaps more than one hard fork. That will introduce a number of changes into the Ethereum system. A couple of big things that are happening, specifically for Byzantium, which is stage one of Metropolis, are the introduction of ZK Snarks, which allows Ethereum to be able to use the technology introduced by Zcash, to do zero-knowledge transactions for very high levels of confidentiality and privacy. The native execution of ZK Snarks has been a goal of Vitalik Buterin for a while now, and it will be introduced with Byzantium. The other very big change introduced with the first stage of Metropolis is the move towards proof of stake. Today, Ethereum operates using a proof-of-work mining algorithm called ET Hash, or ETH Hash. ETH Hash is a mining protocol that uses hashing with the SHA-3 Ketchak 256 algorithm, similar to how Bitcoin does mining with SHA-256, with a few changes that make it a bit more memory-intensive, to prevent the easy development of ASICs. In the first stage of Metropolis, new mechanism will be introduced, which is proof-of-stake. Proof-of-stake will be using a protocol called CASPER. Proof-of-stake is different from proof-of-work, in that it allows validation of transactions without mining, instead using validators, who stake or bet an amount of Ether in the validation of a block. If they validate a block that is broadly accepted by the network, they receive a small reward in proportion to the amount of stake that they bet on the validation of that block. If they approve a block that the rest of the network rejects, then they lose their stake. This mechanism of reward and punishment is different than the mechanism of mining that requires computation with repeated hashing, and is going to be introduced with Byzantium. Ethereum is not going to move directly to proof-of-stake. Instead, in the first stage, it is going to move to a hybrid environment, where it uses proof-of-work and proof-of-stake simultaneously. Another big change that is coming with Byzantium is the diffusing of the difficulty bomb. Ethereum had a planned system within it called the difficulty bomb that was intended to force the developers to move to proof-of-stake by making it increasingly difficult to mine using proof-of-work. That difficulty bomb is expected to increase the validation of blocks from every 14 seconds to more than 15 seconds in the next three months, and then within six months to 28 seconds or more. Then, it will exponentially increase the difficulty until it is impossible to mine transactions on Ethereum. That is obviously not ideal, because due to the delays in the deployment of Metropolis, the difficulty bomb is now upon us. One of the first changes that happens with Byzantium is pushing back the imposed difficulty that the difficulty bomb creates to give more time to deploy proof-of-stake. A couple of other really interesting developments in Metropolis and Byzantium are the introduction of account abstractions, where gradually Ethereum is moving to blur the line between the two account types that are available. At the moment, Ethereum has two types of accounts. There are externally owned accounts, or EOAs, which are accounts that are owned by systems outside of Ethereum, with private public key pairs. Wallets, for example, in Ethereum, are externally owned accounts, and contracts. Contracts are the other type of account where money is managed by the code executed by a smart contract. They have some differences between them, and the way they're validated is different, the way they pay for gas is different. These differences are going to gradually be abstracted so that they behave more and more the same, until eventually Ethereum only has one type of account. There's no difference between an account that has a private key behind it, or some other mechanism for authorization or signing, and an account that's managed by a smart contract code. They will behave identically. Another big change is the introduction of the ability for intermediary accounts to pay for gas. Today, if you run a transaction that executes smart contract code, that transaction has to pay for the gas. The smart contract itself can't pay for the gas. If the smart contract calls another smart contract, which calls another smart contract, then the gas is still paid by the first transaction that initiated this chain of calls. With Byzantium, the intention is to allow intermediate contracts to pay for gas themselves, so you can call a contract with a transaction, and then when that contract calls another contract, it can pay for all or some of that gas. I think that includes most of the changes we'll see in Byzantium, but of course, it's still in flux, and there may be more changes introduced. In Byzantium, maybe some of the changes will be pushed back into Constantinople for the second part of the Metropolis upgrade.