Presents a primer to object-oriented programming techniques that are standards in the software programming industry. It gives a detailed description of each of the 23 GoF (Gang of Four) patterns, refactored from either Boolean logic or less intuitive, maintainable, or scaleable code that you might encounter in the real world, to a particular pattern. Starting in this way -- refactoring from simpler, less maintainable code to a pattern -- shows the reader how to use the pattern in their code. Each patterns section walks the reader through making the move from current code to the pattern, lists the benefits of using the pattern, and shows how the pattern performs after the refactoring effort. The book begins with an introduction that details some history of GoF patterns, briefly explains the reasoning behind patterns, and defines the audience and assumptions. Chapter 1 discusses patterns methodology and gives reasons why readers might want to use patterns in their code. It also addresses some basic object-oriented aspects that are important to understanding the rest of the book, including refactoring, patterns interaction, and basic object-oriented aspects. The remaining chapters discuss the patterns themselves -- Creational Patterns, Behavioural Patterns, and Structural Patterns. The book also includes a glossary of relevant terms. The book is designed for intermediate-level .NET, Java, and C++ programmers who are completely new to GoF design patterns as well as more seasoned programmers who wish to better understand the GoF patterns in detail.