This chapter provides an overview of the evolution and applications of smart contracts across various blockchain platforms, including Ethereum, Hyperledger, and Corda. It begins by defining smart contracts as self-executing digital agreements coded onto the blockchain, operating on principles of immutability, transparency, and decentralization (Szabo 1994; Cong and He 2019). The discussion highlights how different blockchain versions support smart contract functionality and compares their unique features, advantages, and limitations (Zheng et al. 2020). The chapter emphasizes the transformative impact of smart contracts in industries such as decentralized finance (DeFi), where they automate lending, exchanges, and yield farming; in supply chain management for enhanced traceability; and in real estate through tokenization and streamlined transactions. Additional applications in healthcare and identity verification are also explored, showcasing benefits like data security and decentralized identity management. The chapter concludes by addressing ongoing challenges, including security issues, scalability, and regulatory hurdles, while outlining potential advancements and future directions for this rapidly evolving technology.