There is a growing trend of adopting blockchain technologies to the industrial Internet of Things (IIoT) due to the traceability, nonrepudiation, and immutability of blockchain systems. The proliferation of IIoT to industrial systems is fostering the fourth industrial revolution (aka Industry 4.0) while IIoT also confronts several challenges exhibiting in the following two perspectives: 1) security and privacy protection of IIoT data; 2) interoperability absence across IIoT systems. Blockchain and blockchain-enabled smart contracts can essentially offer solutions to address the emerging challenges in IIoT. The objective of this special section in IEEE Transactions on Industrial Informatics is to explore the state-of-the-art advances in adopting blockchain technologies for IIoT.