We are surrounded by interactive devices, artifacts, and systems. The general assumption is that interactivity is good -- that it is a positive feature associated with being modern, efficient, fast, flexible, and in control. Yet there is no very precise idea of what interaction is and what interactivity means. In this book, Lars-Erik Janlert and Erik Stolterman investigate the elements of interaction and how they can be defined and measured. They focus on interaction with digital artifacts and systems but draw inspiration from the broader, everyday sense of the word.Viewing the topic from a design perspective, Janlert and Stolterman take as their starting point the interface, which is designed to implement the interaction. They explore how the interface has changed over time, from a surface with knobs and dials to clickable symbols to gestures to the absence of anything visible. Janlert and Stolterman examine properties and qualities of designed artifacts and systems, primarily those that are open for manipulation by designers, considering such topics as complexity, clutter, control, and the emergence of an expressive-impressive style of interaction. They argue that only when we understand the basic concepts and terms of interactivity and interaction will we be able to discuss seriously its possible futures.