As the internet of things (IoT) and industrial internet of things (IIoT) continue to expand, the need for robust cyber security solutions becomes increasingly critical. The convergence of blockchain technology and artificial intelligence (AI) offers promising opportunities to address the security challenges posed by IoT and IIoT applications. This chapter provides an overview of the potential synergies between blockchain and AI in the context of cyber security for IoT and IIoT. Blockchain technology, with its decentralized and immutable nature, can provide enhanced security and trust in IoT and IIoT networks. It offers features such as data integrity, transparency, and tamper resistance, making it well-suited for securing critical data and transactions. Additionally, blockchain can facilitate secure device identity management, access control, and secure communication among IoT and IIoT devices.