Advances in the domain of electronics and information and communication technology provide a tremendous set of new possibilities and services. The development of the Internet of Things concept where different sensors, actuators, and control devices are connected together and where functions are provided to the Internet, is on the way to be used also in various industrial domains. A new age of intelligence in such industrial systems is being formed. Hence, the aim of this work is to provide an overview about ongoing research and technology developments related to the digitalization of industrial systems applying the IoT approach. This review covers the domain of manufacturing, as an example for discrete systems, and the power and energy domain, as an example for continuous systems. Important domain standards and future research directions are identified and discussed also.