Blockchain architecture is a promise of finality and non-repudiation. It has distinct advantages over the traditional client-server or distributed systems, which have made various organizations explore use cases where blockchain can be applied. This chapter explores the key nuances of the blockchain architecture. It begins with an overview of the hash functions, hashing and how it plays an important role in blockchain architecture. While blockchain is well known as a P2P architecture, the chapter explores other aspects of the blockchain architecture, which are responsible for the strength of the blockchain. The chapter presents a deep dive into the block structure, use of Merkle trees for transactions and the blockchain structure. The power of decentralization, the built-in redundancy in the blockchain architectures and how it helps establish a trustless system is explained. It presents the challenges of distributed consensus and how they are dealt with via various consensus algorithms in the blockchain architecture. The chapter ends with a sample use case discussion of Maintenance and Service Supply Chain over a permissioned blockchain architecture using Hyperledger framework.