Informed by our physical interactions with paper, Google designed a visual system to unify their product experiences with those of Android. Adapting the behaviours implicit to paper and translating them into digital surfaces, Google built generative systems that create shadows dynamically, more natural interaction patterns and responsive surfaces. Building on classic principles of print design, content is front and centre. Surfaces and shadows establish a physical structure that intuitively explains hierarchy and interface interactions. Material Design was introduced with the Android Lollipop operating system and evolving design documentation lives online.