“Design is not just what it looks like and feels like Design is how it works.” This famous quote from Steve Jobs stresses the importance of having good interaction design, which is the user’s overall experience and satisfaction with a product.

And no company embodies this better than Apple. But what exactly is HCI and interaction design? Is it the same as UX? And what do interaction designers do anyway? Read on to find the answers to these questions and learn more about interaction design.

What is interaction design?

Interaction design, often abbreviated as IxD, is the practice of designing interactive digital products and services. John Kolko, Author of Thoughts on Interaction Design, gives the following definition to interaction design: “Interaction Design is the creation of a dialogue between a person and a product, system, or service. This dialogue is both physical and emotional in nature and is manifested in the interplay between form, function, and technology as experienced over time.

Interaction designers focus on the way users interact with products and they use principles of good communication to create desired user experiences.

Interaction design and user experience

The term “interaction design” is sometimes used interchangeably with “user experience design.” That’s understandable because there’s a huge overlap between interaction design and UX design. After all, UX design is about shaping the experience of using a product, and a major part of that experience involves interaction between the user and the product. But interaction design and user experience aren’t synonymous.

The key difference between UX and interaction design is in the way we think about user interactions. Interaction designers are focused on the moment when a user interacts with a product and their goal is to improve the interactive experience. For UX designers, the moment of interaction is just a part of the journey that a user goes through when they interact with a product. User experience design accounts for all user-facing aspects of a product or system.

interaction design model
Interaction design is a part of UX design. Image by Dan Saffer.

UX design and interaction design are connected but it’s nearly impossible to create good interaction design in isolation of UX. Interaction design is a spoke in the umbrella of user experience (UX design).

umbrella model showing how UX solves problems
How UX solves problems. Image by Dan Willis.

The five dimensions framework

The five dimensions of interaction design is a useful model for understanding what interaction design involves. Gillian Crampton Smith, an interaction design academic, first introduced the concept of four dimensions of an interaction design language. Kevin Silver later extended his model with the fifth dimension.

IxD involves words (1D), visual representations (2D), physical objects/space (3D), time (4D), and behavior (5D).

  • 1D: Words. Words encompass text, which helps convey the right amount of information to users. Words, especially those used in interactions, like button labels, should be meaningful and simple to understand. They should communicate information to users without overwhelming them with too many details.
  • 2D: Visual representations. Visual representations include typography, icons, and other graphics with which users interact. Visual representations usually supplement the words used to communicate information to users.
  • 3D: Physical objects or space. Physical objects are a medium through which users interact with the product or service. For instance, a user interacts with computers and a mouse while sitting on a desk in an office space.
  • 4D: Time. Time helps users understand visual changes in a UI; it also helps users track their progress.
  • 5D: Behavior. Behavior includes both action and reaction. Behavior is what describes the mechanism of an interaction with a product.

Interaction designers should utilize all five dimensions to consider the interactions between a user and a product in a holistic way.

Cover of interaction design course
5 dimensions of interaction design. Image by Interaction Design.

Interaction design principles

While it’s impossible to list all of the principles of interaction design, it’s still possible to describe a few general areas that are widely used in this field:

Goal-driven design

Goal-driven design is a design style that holds problem-solving as the highest priority. This approach focuses on satisfying the specific needs and desires of a person who will use the product, which is the goal of interaction design.

Good usability

Usability answers the question “can people use this product?” Good usability is a fundamental requirement for interaction design. Learnability (how easily can a new user learn to use the interface?), efficiency (how quickly can users perform tasks?), error rate (how many errors do users make while interacting with UI?) as well as error-recovery (how quickly can they recover from errors?) are four things that have a direct impact on usability.

It’s possible to measure usability using task-completion time and overall satisfaction (do users enjoy using the product).

When it comes to actual design decisions, interaction designers often familiarize themselves with the user’s mental model – the perception or representation that a person has in his mind of the product she is interacting with. The knowledge they gain from the mental models helps them create UX design systems that feel intuitive.


Interaction designers apply physiological principles to the design of products. The goal of this process is to reduce human error, increase productivity, and enhance the safety of interaction. Interaction designers often use a predictive model of human movement, also known as Fitts’s law, when they design interactions. This law says that the time required to rapidly move to a target area is a function of the ratio between the distance to the target and the width of the target. Fitts’s law is used to model the act of pointing. It can be applied both when the UI element is touched with a hand or finger, or virtually, using a pointing device.

illustration of Fitt's law
Illustration of Fitts law

Positive emotional responses

Designers must create a design that influences positive emotional responses in users. Interaction designers are aware of elements that influence user emotional responses. Color palettes, fonts, animations—all of them can trigger emotional responses.

Design for people

When it comes to product design, it’s hard to design for an abstract user. Designers should always evaluate their decision in the context of a particular user group. Personas are a great tool for designers.

A persona encapsulates critical data about a user group in a way that designers can understand and relate to. The emotional aspects influence designers to create better product behavior.

Example of a user persona
Image by xtensio

Design patterns

How do designers address interaction problems? They use patterns. A pattern is a solution for a particular context. In many situations, designers can address new problems through the modification of existing patterns. The goal of interaction design is to create a solution that fits well in the context of use.

Usually, interaction designers start with well-known interface guidelines such as Human Interface Guidelines by Apple and Material Design by Google. The guidelines not only provide the patterns that are familiar for the users but also show how to use them in specific contexts.

Design iterations

Designers can have multiple solutions for one particular interaction problem. The only correct way to reduce the number of design options is to see how it works for real users (validate it through testing). Not all assumptions about interaction design pass the testing. Quite often, designers have to return to the drawing board to design an alternative solution. That’s why interaction design is rarely linear, but an iterative process.

Role of an interaction designer

After resting all the information, you might still wonder, “What do interaction designers really do?” There is no single correct answer to this question. As a separate role, “interaction designer” exists primarily in large organizations such as Google and Apple, but in smaller organizations, the responsibilities of an interaction designer are distributed between UI and UX designers.

Generally, the responsibilities of the interaction designer include identifying key interactions of the product and creating prototypes to test concepts. Here are two areas where the impact of interaction designers is especially significant:

  • Design strategy. The interaction designer always starts with understanding what the target user is trying to accomplish (their goals) and finding interactions that will help to achieve those goals. Interaction designers might have to conduct user research to find out those goals.
  • Prototyping tools. Interaction designers often create interactive prototypes to lay out the interactions.  Sometimes, in order to make the interaction obvious for the user, interaction designers create interactive prototypes that look exactly like the actual products.

Interaction designers work together with other designers (UX and visual designers) to ensure that all interaction patterns are implemented correctly in a product. Interaction designers should always be on top of the current technological trends and always measure them in the context of value they deliver to users.

Best practices for designing interactions

Usability.gov suggests asking the following questions when creating digital products that have an interactive element:

  • What commands can a user give to interact with the interface?
  • What about the appearance (color, shape, size, etc) gives the user a clue about how it may function?
  • What information do you provide to let a user know what will happen before they perform an action?
  • Are there constraints put in place to help prevent errors?
  • Do error messages provide a way for the user to correct the problem or explain why the error occurred?
  • What feedback does a user get once an action is performed?
  • How long between an action and a product’s response time?
  • Are the interface elements a reasonable size to interact with?
  • Are edges and corners strategically being used to locate interactive elements like menus?
  • Is information chunked into a few items at a time?
  • Are familiar formats used?


Digital design is a conversation. This conversation happens between a machine and a person who uses it. When people interact with a product, they love having smooth interactions, but it only happens when interaction designers make things right.