The practice of designing the behaviors and responses of digital products — how they respond to user input, how transitions communicate change, and how the system conveys its state over time. Interaction design shapes the moment-to-moment experience of using a product, distinct from visual design (how it looks) and information architecture (how it is organized).
Common contexts
- Mapping every state a form field can enter — empty, focused, filled, error, disabled — before handing off to engineering
- Defining transition behaviors between a list view and a detail view to preserve spatial orientation
- Prototyping drag-and-drop reordering gestures to validate the interaction model before visual design begins
Use when
Make IxD decisions explicit when handing off to engineers — document all component states, transitions, and edge cases, because undocumented behavior gets implemented inconsistently.
Avoid when
Don't treat interaction design as decoration added after visual design is finished — retrofitting logical behavior onto a completed visual structure almost always produces inconsistencies.
Most interaction design debt isn't visible in mockups — it lives in the undocumented edge cases that engineers and developers have to guess their way through at 11pm.
Real-world examples
- Apple's swipe-to-unlock gesture (2007) established a touchscreen interaction paradigm that every Android manufacturer subsequently adopted, defining the grammar of smartphone IxD.
- The pull-to-refresh gesture, created by Loren Brichter for Tweetie in 2008, became so canonical it was adopted by every major social feed app and later codified in Apple's Human Interface Guidelines.
- Google Material Design's 'ripple' touch feedback animates outward from the precise point of contact, providing spatial confirmation that maps user action to on-screen response.