The field of the Industrial Internet of Things (IIoT) is developing rapidly and gaining abundant attention throughout our society. The vast volume of raw information that these IoT devices generate opens the door for an evolving field that draws useful insights from raw data. This area of study that deals with the extraction of information and draws insights from IoT data using various algorithmic and scientific methods is called data science. This field is in high demand among various industries and academic institutions. However, due to the lack of fundamental security technology, vulnerabilities and security risks are emerging in these IoT devices. Therefore, there is a need to secure and store such extracted data and insights, since this information can be sensitive and must be tamper-proof. Blockchain technology is being used as a decentralized and distributed approach to ensure the security requirements of IoT, enhance IoT and IIoT development, and as an immutable storage system. However, scalability and transaction fees are the major challenges that restrict the use of blockchain technology for IIoT. This chapter introduces a Directed Acyclic Graph (DAG)-based blockchain called IOTA, which overcomes these major challenges of the traditional blockchain to enable seamless integration with IoT devices. Furthermore, three IIoT applications are proposed and elaborated, consisting of (1) Device Identity Management, (2) Sensor data anomaly detection using Artificial Intelligence (AI), and (3) Security of IIoT data using IOTA Tangle.