This chapter delves into the technological foundation that makes blockchain a secure, decentralized, and transparent system. Cryptographic techniques, such as hash functions and public key cryptography, play a critical role in ensuring data integrity and authenticity. The chapter also highlights two major consensus mechanisms—Proof of Work and Proof of Stake—contrasting their energy consumption and security implications. Furthermore, the chapter explores the functionality of smart contracts and decentralized applications, with real-world examples like health insurance claim processing and MediBlock. These technologies form the building blocks for blockchain’s transformative potential in healthcare and other industries. By expanding on the core blockchain technologies, this chapter equips the reader with the foundational knowledge needed to understand blockchain’s role in secure and decentralized systems, especially in sensitive applications like healthcare.