This chapter presents a comprehensive exploration of information systems (IS), analyzing their role, structure, and life cycle. First, we clarify key concepts such as data, information, and knowledge and explain their interconnections within organizations. The discussion thus defines IS from both a technological and an organizational point of view, underlining its importance in modern business environments. In this chapter, we describe the IS life cycle in detail, covering the planning, design, development, testing, and maintenance phases. We also introduce the information and knowledge management layer, highlighting data analysis and information extraction as critical components for turning raw data into useful information. Finally, the chapter discusses information systems engineering (ISE) as an interdisciplinary approach integrating technical and business considerations, addressing the challenges of big data, automation, and security. By examining methodologies, technologies, and best practices, this chapter provides a structured framework for understanding and optimizing IS in dynamic organizational contexts.