Every web application needs a place to store and retrieve its data—user accounts, product listings, chat messages, you name it. In this chapter we explore the two big families of databases that power modern web apps: the structured, table‑driven world of SQL and the flexible, document‑oriented world of NoSQL. You’ll learn what each one does well, how to use them from a Node.js backend, and how to make them fast and reliable as your application grows.