A genesis block is the first block of a blockchain, i.e., the very first block upon which additional blocks are appended over time subject to the applicable validation or mining process. Early versions of blockchain (Bitcoin blockchain) initiated counting from 1 (block 1). Later versions number genesis block as block 0.

The genesis block initiates a blockchain by setting up the network, subject to consensus rules, and linking all additional blocks to the origination point.

The genesis block has no predecessor, as it is the first in the sequence of blocks that will be added to the network. A block is a collection of transactions that are recorded and validated together. The transactions in each block are added all at once to the network, which maintains a full historical record of validated transactions.

Every blockchain has its own genesis block, out of which the features of later blocks are derived in accordance with the mining process. The genesis block is usually hardcoded into the software of the applications that function and operate on its blockchain.

A blockchain is the structure that represents a decentralized, distributed and public digital ledger where transactions across a network are recorded and verified subject to a consensus building process. The records cannot be adjusted retroactively without adjusting all subsequent blocks and the consensus established across the respective blocks. Network nodes construct transactions into blocks, and if the transactions are successfully validated by the blockchain, blocks will be appended to the blockchain. Each block contains a number of transactions which represent the activity that’s recorded on the blockchain.

Validation (or mining) is the process of selecting transactions for inclusion into a block. It is performed by a node on the network known as a validator or miner. Nodes aggregate the transactions which are submitted to the blockchain. After validation, transactions are proposed to the next block on the blockchain. Selection of a block depends on the consensus mechanism adopted by the network.