Qtum connects Bitcoin, Ethereum, and real-world data.

Bitcoin and Ethereum, two mainstream blockchains, use different approaches to store the information about wallet balances on the ledger.

Bitcoin employs unspent transaction outputs, or UTXO. Each transaction has a set of inputs and outputs. When a new transaction is made, bitcoin wallet first picks the output that wasn’t previously spent on some other transaction and makes it the input of a new transaction.

Ethereum uses an account-based system, which is similar to the bank accounts. Each wallet has a balance, which is basically a sum of all ether. When someone sends ether to the wallet, the balance increases. When wallet user sends ether to someone else, the balance decreases.

Qtum achieves compatibility with the other blockchains. Qtum is compatible with Bitcoin by design, as its code is based on Bitcoin code. To be compatible with Ethereum, Qtum need to convert UTXO-based transactions into account-based ones. Qtum achieves that with Account Abstraction Layer, the middleware between two systems.

Most of the blockchain systems today are closed systems, i.e. they don’t interact with outside world. Qtum wants to connect business data with the blockchain. To accomplish that, it utilizes the concepts of a data feed, an oracle, and master contract. Data feeds are various data sources outside of the blockchain. It can be a data from thermometer or a currency exchange rate. Oracle is an organization or a program that selects the most suitable data source when there are many of them are available. For example, if five thermometers report their measurements, an oracle can pick an average result. Finally, master contracts are smart contracts that can be triggered by off-chain data. An example of a master contract is a program that turns heating on when the temperature is below some number.

Qtum expands blockchain infrastructure with Go Mobile strategy. UTXO-based model, used by Qtum, allows using SPV (Simplified Payment Verification) protocol. This protocol allows building lite wallets. Lite wallets don’t need to store the whole blockchain to verify their transactions. That way, Qtum is the first blockchain where lite wallets can execute smart contracts in a trustless way, without downloading the full blockchain. This allows executing smart contracts on smartphones and IoT devices.


  • December 19, 2016: Launch on Bitcointalk bitcointalk.org
  • March 16, 2017—March 21, 2017: Qtum ICO twitter.com
  • March 17, 2017: Partnership with BloqLabs. BloqLabs supports important open-source blockchain projects. qtum.org
  • June 28, 2017: First Qtum release on Github. This release is for Sparknet, first Qtum testnet github.com
  • September 13, 2017: Mainnet launch blog.qtum.org
  • December 19, 2017: Qtum awarded $250,000 to Trusted IoT Alliance. Trusted IoT Alliance blog.qtum.org
  • January 19, 2018: Banca announced to build on Qtum. Banca’s team plan to build an investment bank on the blockchain. blog.qtum.org
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