In this day and age, data have become an immensely valuable resource. They are the key driver that puts the smart into smart services. This is fundamentally fueled by two technological achievements, namely the Internet of Things (IoT), which enables continuous and comprehensive collection of all kinds of data, and blockchain technologies, which provide secure data management and exchange. In addition to those information security measures, however, data privacy solutions are also required to protect the involved sensitive data. In this Special Issue, eight research papers address security and privacy challenges when dealing with blockchain technologies and the IoT. Concerning the IoT, solutions are presented on how IoT group communication can be secured and how trust within IoT applications can be increased. In the context of blockchain technologies, approaches are introduced on how the capabilities of query processing can be enhanced and how a proof-of-work consensus protocol can be efficiently applied in IoT environments. Furthermore, it is discussed how blockchain technologies can be used in IoT environments to control access to confidential IoT data as well as to enable privacy-aware data sharing. Finally, two reviews give an overview of the state of the art in in-app activity recognition based on convolutional neural networks and the prospects for blockchain technology applications in ambient assisted living.