Nowadays, learning and applying design patterns is an important aspect of software engineering. Design patterns are like water – you can't live without them. Don't believe me? Just ask hiring managers, and you will find that many of them have design patterns in their job postings as well as related questions in job interviews. It is a common belief that design patterns are important ingredients for software development and everyone should know them.

In this chapter, we will provide some context about why design patterns are useful and how they have served us well in the past few decades. By understanding the motivation behind design patterns, we will be able to set forth a set of guiding principles for developing software. The following topics will be discussed in this chapter:

• The history of design patterns 
• Software design principles
• Software quality objectives