This chapter presents a comprehensive overview of blockchain technology and its application in cryptocurrencies. It begins with the fundamentals of blockchain, covering its definition, operational mechanisms, types, consensus models, smart contracts, and evolutionary trajectory, while also addressing its inherent limitations and challenges. The discussion then extends to cryptocurrencies, explaining their creation through mining, transaction processes, wallets, keys, and major global digital currencies. Critical issues such as risks, regulatory frameworks, and future directions of cryptocurrencies are highlighted. The chapter further explores practical applications of blockchain across finance, supply chains, healthcare, and governance, alongside broader challenges to adoption. Ethical, security, and sustainability considerations, including privacy, cybersecurity, and environmental impacts, are examined. Finally, emerging trends such as Web3, decentralised finance (DeFi), non-fungible tokens (NFTs), central bank digital currencies (CBDCs), and cross-chain interoperability are discussed, supported by real-world case studies of blockchain deployments. This chapter serves as both an introduction and a forward-looking analysis of blockchain’s transformative potential and its implications for the digital economy.