This chapter explains how databases are used in web applications to organize and retrieve information efficiently. To make database systems work well, it's crucial to follow specific rules, like normalization. If these rules aren't followed, the database might not perform as well and require more time to set up. There are software tools called database access interfaces that help programs connect to databases. The chapter also shows how web applications are built using databases to handle a lot of data at once and share it with users in different locations.