In this chapter, we start by zooming out and review the database design process. We elaborate on conceptual, logical and physical database design. We continue the chapter with conceptual design which aims at elucidating the data requirements of a business process in a formal way. We discuss three types of conceptual data models: the ER model, the EER model and the UML class diagram. Each model is first defined in terms of its fundamental building blocks. Various examples are included for clarification. We also discuss the limitations of the three conceptual data models and contrast them in terms of their expressive power and modeling semantics.