Interaction design, often abbreviated as IxD, is "the practice of designing interactive digital products, environments, systems, and services.":xxxi,1 While the digital side of this statement is true, interaction design is also useful when creating physical (non-digital) products, exploring how a user might interact with it. Common topics of interaction design include design, human–computer interaction, and software development. While interaction design has an interest in form (similar to other design fields), its main area of focus rests on behavior.:1 Rather than analyzing how things are, interaction design synthesizes and imagines things as they could be. This element of interaction design is what clearly marks IxD as a design field as opposed to a science or engineering field.:xviii
While disciplines such as software engineering have a heavy focus on designing for technical stakeholders, interaction design is geared toward satisfying the majority of users.:xviii
The term interaction design was coined by Bill Moggridge and Bill Verplank in the mid-1980s, but it took 10 years before other designers the concept started to take hold.:xviii To Verplank, it was an adaptation of the computer science term user interface design for the industrial design profession. To Moggridge, it was an improvement over soft-face, which he had coined in 1984 to refer to the application of industrial design to products containing software.
The earliest programs in design for interactive technologies were the Visible Language Workshop, started by Muriel Cooper at MIT in 1975, and The Interactive Telecommunications Program founded at NYU in 1979 by Martin Elton and later headed by Red Burns.
The first academic program officially named "Interaction Design" was established at Carnegie Mellon University in 1994 as a Master of Design in Interaction Design. At the outset, the program focused mainly on screen interfaces, before shifting to a greater emphasis on the "big picture" aspects of interaction—people, organizations, culture, service and system.
In 1990, Gillian Crampton Smith founded the Computer-related Design MA at the Royal College of Art (RCA) in London, changed in 2005 to Design Interactions, headed by Anthony Dunne. In 2001, Crampton Smith helped found the Interaction Design Institute Ivrea, a small institute in Olivetti's hometown in Northern Italy, dedicated solely to interaction design. The institute moved to Milan in October 2005 and merged with Domus Academy. In 2007, some of the people originally involved with IDII set up the Copenhagen Institute of Interaction Design (CIID). After Ivrea, Crampton Smith and Philip Tabor added the Interaction Design (IxD) track in the Visual and Multimedia Communication at Iuav, University of Venice, Italy, between 2006 and 2014.
Goal-oriented design (or Goal-Directed™ design) "is concerned with satisfying the needs and desires of the users of a product or service.":xviii
Alan Cooper argues in The Inmates Are Running the Asylum that we need a new approach to solving interactive software-based problems.:1 The problems with designing computer interfaces are fundamentally different from those that do not include software (e.g., hammers). Cooper introduces the concept of cognitive friction, whereby we anthropomorphize (treat as human) products that are complex enough that users cannot always understand how they behave. Computer interfaces often qualify.:22
Alternatively, interfaces can be designed to serve the needs of the service/product provider. User needs may be poorly served by this approach.
Usability answers the question "can someone use this interface?". Jacob Nielsen describes usability as the quality attribute  which describes how usable the interface is. Shneiderman proposes principles for designing more usable interfaces called "Eight Golden Rules of Interface Design" which are well known heuristics for creating usable systems.
A persona encapsulates critical behavioural data in a way that both designers and stakeholders can understand, remember and relate to. Personas use storytelling to engage users' social and emotional aspects, which allows designers to either visualize the best product behaviour or see why the recommended design is successful.
The cognitive dimensions framework provides a vocabulary to evaluate and modify design solutions. Cognitive dimensions offer a lightweight approach to analysis of a design quality, rather than an in-depth, detailed description. They provide a common vocabulary for discussing notation, user interface or programming language design.
Dimensions provide high-level descriptions of the interface and how the user interacts with it: examples include consistency, error-proneness, hard mental operations, viscosity and premature commitment. These concepts aid the creation of new designs from existing ones through design maneuvers that alter the design within a particular dimension.
Designers must be aware of elements that influence user emotional responses. For instance, products must convey positive emotions while avoiding negative ones. Other important aspects include motivational, learning, creative, social and persuasive influences. One method that can help convey such aspects is for example, the use of dynamic icons, animations and sound to help communicate, creating a sense of interactivity. Interface aspects such as fonts, color palettes and graphical layouts can influence acceptance. Studies showed that affective aspects can affect perceptions of usability.
Emotion and pleasure theories exist to explain interface responses. These include Don Norman's emotional design model, Patrick Jordan's pleasure model and McCarthy and Wright's Technology as Experience framework.
The concept of dimensions of interaction design were introduced in Moggridge's book Designing Interactions. Crampton Smith wrote that interaction design draws on four existing design languages, 1D, 2D, 3D, 4D. Silver later proposed a fifth dimension, behaviour.
This dimension defines interactions: words are the element that users interact with.
Visual representations are the elements of an interface that the user perceives; these may include but are not limited to "typography, diagrams, icons, and other graphics".
This dimension defines the objects or space "with which or within which users interact".
The time during which the user interacts with the interface. An example of this includes "content that changes over time such as sound, video or animation".
Behaviour defines and how user respond to the interface.
The Interaction Design Association was created in 2003 to serve the community. The organization has over 80,000 members and more than 173 local groups. IxDA hosts Interaction the annual interaction design conference, and the Interaction Awards.