Every AppleScript program is a script. This chapter describes the structure of a script. A script is composed of certain definite building blocks, and they go together in a certain way. The next several chapters will return to each of these building blocks individually and explain them in full detail, but first we need an introduction to the entire cast of characters that constitute a script. That's what this chapter is for. It provides the crucial overall map of a script's world, so that in our explorations during subsequent chapters you'll know where we're going and how the geography fits together.