This document provides an overview of how blockchain technology can be used to enhance security and privacy in IoT networks. It discusses some of the key challenges with centralized IoT systems, such as lack of user control over data and single points of failure. Blockchain offers a decentralized alternative that allows for immutable and traceable records, authentication without single authorities, and more scalable networks. The document reviews benefits of blockchain for IoT like increased trust, transparency and security. It also provides illustrations of blockchain structure and how blocks are interconnected in a blockchain.