The chapter introduces the entity-relationship (ER) model, a data model that incorporates semantic information from the real world. It presents a diagrammatic technique for representing entities and relationships and provides an example of database design using this model. The author discusses the implications of the ER model on data integrity, information retrieval, and data manipulation. Additionally, the ER model is proposed as a unifying framework for different data models, including the network model, relational model, and entity set mode, addressing semantic ambiguities in these models. The chapter also explores the structured design of relational and network databases using the ER approach.The chapter introduces the entity-relationship (ER) model, a data model that incorporates semantic information from the real world. It presents a diagrammatic technique for representing entities and relationships and provides an example of database design using this model. The author discusses the implications of the ER model on data integrity, information retrieval, and data manipulation. Additionally, the ER model is proposed as a unifying framework for different data models, including the network model, relational model, and entity set mode, addressing semantic ambiguities in these models. The chapter also explores the structured design of relational and network databases using the ER approach.