This book is an introduction to the study of programming languages. The material has evolved from lecture notes used in a programming languages course for juniors, seniors, and graduate students at Johns Hopkins University.

The book treats programming language topics from a foundational, but not formal, perspective. It is foundational in that it focuses on core concepts in language design such as functions, records, objects, and types and not directly on applied languages such as C, C++, or Java. We show how the particular core concepts are realized in these modern languages, and so the reader should emerge from this book with a stronger sense of how they are structured.

The book is not formal in the sense that no theorems are proved about programming languages. We do, however, use several techniques that are useful in the formal study of programming languages, including operational semantics and type systems. With these techniques we can define more carefully how programs should behave.