Something that is constant and cannot be adjusted or revised. In technology and data, immutability usually refers to the incapacity to modify or tamper with data once assembled or documented. In the domain of blockchain technology, immutability is an essential attribute. Blockchain is a decentralized and dispersed ledger that registers transactions and data in blocks. Once a block is added to the blockchain, it becomes permanent and cannot be modified retroactively without agreement from the network participants.