This chapter introduces fundamental concepts related to the application domain within the context of Industry 4.0 and predictive maintenance. It covers cyber-physical production systems (CPPSs), common faults and failures, maintenance approaches to prevent them, and the role of learning factories in research. The following four sections discuss the key technologies applied later in the book: Semantic Web technologies for representing expert knowledge, time series analysis techniques, machine learning–particularly neural networks for time series and knowledge graphs–as well as case-based reasoning.