Design by concept is a new approach to creating software. A software product--whether an app, a service or a system--is viewed as a collection of interacting concepts, each with its own purpose, structure and behavior. Concepts can be invented afresh, but they can also be reused, exploiting the knowledge embodied in previous successful designs.This book explains what concepts are and why they are central to software design; shows examples of concepts (from the most effective and ingenious to the most flawed and frustrating) taken from well-known applications; and presents design principles that can identify and eliminate flaws in existing and new designs.