Welcome and congratulations on your entry to this course in database systems. The fact that you are in this course means that you have covered several fundamental topics in programming, data structures, user interface, and software engineering. Now you want to learn about databases—their significance, the underlying theoretical principles that govern them, how they are constructed, and their management. You are at the right place. This chapter addresses the first issue: the significance of database systems. The sections in this chapter are the following.