Digital technology is fundamentally altering the world we live in, but can only be truly understood in relation to the physical world we all inhabit. The most successful future products and policies will be those that take this rich digital/physical ecology seriously. The physical world is increasingly filled with digital products to the extent that the boundaries of digital and physical reality become blurred. From mundane devices such as mobile phones and washing machines, to esoteric research including tangible computation and body implants, we continually bridge two worlds literally touching buttons and dials and simultaneously interacting with the digital systems that lie behind them. The connection between pure thought and abstract information is through solid keyboard and mouse; but likewise the material world of buildings, cars and running shoes is suffused with computation through sensors, displays and flashing LEDs. How do people understand this world and how can designers create usable hybrid physical-digital products? TouchIT brings together insights from human-computer interaction and industrial design, exploring these themes under four main headings: human body and mind; objects and things; space; and information and computation. In considering each, the authors look into the underlying physical processes, our human understanding of them, and then the way these inform and are informed by digital design. The end draws together the theoretical and practical implications of this for design, including practical advice, potential tools, and philosophical underpinnings.