As the web continues to change rapidly and become more complex, thinking of it in terms of static pages has become untenable, and many of us have started to approach design in a more systematic way. And yet not all design systems are equally effective. Some can generate coherent user experiences, others produce confusing patchwork designs. Some inspire teams to contribute to them, others are neglected. Some get better with time, more cohesive and better functioning; others get worse, becoming bloated and cumbersome. What are the key qualities of a well-functioning, enduring design system? This question intrigued me so much I spent a huge amount of time researching and thinking about it. My research and thoughts provide the basis of this book.