Database Theory is a field of study that focuses on how data is stored, organized, and accessed in computer systems. It involves understanding the principles behind databases, which are structured collections of data that allow for efficient retrieval and management. Key concepts include data models, schemas, and query languages like SQL. The theory also explores how to ensure data integrity, security, and consistency. It examines various types of databases, such as relational databases and NoSQL databases, each with unique characteristics and use cases. Overall, Database Theory provides the foundation for designing and implementing effective data management systems.